The default bans assume that you're running a non-whitelisted, grief-free, public server with PvP disabled. So then, these defaults assume you want to:
- Prevent or Undo Grief
- Protect your Economy
- Eliminate Unsanctioned PvP
So the defaults are for maximum protection. If any of the above assumptions about your priorities as a server owner aren't correct, then by all means reduce the bans, but first read to make sure you understand WHY each ban is in place. Otherwise, there may be irreparable damage done.
Common Reasons for Bans
Tekkit is a collection of mods which were originally designed for single player, and later shoved into multiplayer without any redesign considerations. That's the reason why everyone talks about what items should be banned and which should not - because as soon as you put two players together playing Tekkit, there's the possibility for one player to completely ruin the other player's fun, even with other plugins (like anti grief) in play.
Even a whitelisted server with great anti grief tools which is shared by friends is on borrowed time, because eventually somebody will get all the stuff they want, get bored, and start "having fun" with their new destructive toys. In many cases, it's impossible to roll back damage or limit the amount of damage, because many Tekkit items completely bypass all plugins, including anti grief and block change loggers. This means resetting or restoring from backup would be your only options, so many items MUST be banned to avoid those situations. When the world gets reset, EVERYONE starts over. When the world is restored from a backup, EVERYONE is set back.
Single player doesn't have a concept of grief, because anything you destroy is either yours or nobody's, so nobody cares what you blow up, wipe out, set on fire, crush, kill, or flood. Tekkit mods were built on that assumption, so many of their items don't bother to play by the rules. On real servers, players want to know that their builds will be protected from jerks who just want to ruin everyone else's fun ("griefers").
There are two types of tools for anti grief. First, the server files backup, which can only be used as a last resort because it will roll back ALL players when it's used. So it's a poor solution.
The second is anti-grief plugins built on the Bukkit platform, either the rollback (ugh!) or preventative (woohoo!) variety. Unfortunately, MANY Tekkit items, especially those from Equivalent Exchange, completely bypass anti grief to do whatever they want anywhere they want, and without leaving any evidence behind to indicate who done it. It's actually impossible for plugins to record or limit changes to the world done by many items, and so they MUST be banned to prevent irreparable damage to player builds and wilderness areas alike.
Single player doesn't have the concept of an economy because there's only one player, so many features could easily ruin a server economy. Consider the simple example of industrial craft, where sunlight is converted into energy, which is then converted into UU matter, which can be crafted into diamonds. With enough preparation, any player can create an unlimited source of diamonds which only requires him to stand around and wait for them to fill up a chest. Of course he doesn't need ALL those diamonds, so he starts giving them away, and there goes your economy.
The sheer level of destruction that some items create (nukes, nuclear reactors, infernal armor, catalytic lens...) is absurd. For a little (or zero, in some cases) cost to the user, these instantly wipe out huge swaths of the world, leaving immense craters, tunnels, trenches, chasms, and worse. It's fine if you're playing single player because it's your world, but when you share a server with others, it's decidedly not cool. So some items are banned just because players can't be trusted to use them thoughtfully.
Note that most of the explosives are NOT on the ban list, because good anti grief plugins (like GriefPrevention) can either prevent or roll back those changes. Further, there's a default safety setting in this plugin which prevents explosives from damaging the surface of your world, so the worst case scenario is a player making a mess somewhere underground where nobody will see. If you disable that safety feature, I strongly recommend you add high explosives to your ban list, and even your world ban list to remove any which may have already been placed somewhere.
I have not banned any items (by default) for sake of "balancing" the game. You may, for example, like to ban the infernal boots because you don't like the idea of anybody flying around indefinitely at zero cost. I'm only placing items on the default ban list when they have the potential to ruin another player's fun (you're allowed to ruin your own fun by taking all challenge out of the game if you like).
Equivalent Exchange Bans
Before you unban an equivalent exchange item, learn how it works. Especially try out the R, C, and G keys (and be sure you have a charged Klein Star in your inventory), and read the EE wiki to learn about it. I did this before I added to them to the ban list, and so I have very good, tested information backing up my default bans.
Players will whine and complain about so many EE items being banned, because they want to become invincible gods who lay waste to continents, hurl thunderbolts from the sky, and crap diamonds. You can't allow this kind of behavior, because it will ruin the fun for everybody else on your server. Tell those players to play single player, or start up their own server and ruin that instead.
Pretty much all of the power items have an extreme world-changing power which completely bypass Bukkit plugins altogether, dodging both anti grief and change logging. Unfortunately, most of them have a secondary fire (usually R or C or G key by default), making it impossible for any plugin to prevent them from being used once a player has them. Therefore, most of the power items are completely banned (no crafting, usage, or ownership without explicit permission).
Magical Rings and Tools
The Black Hole Band is banned due to a duplication bug in EE which allows players to duplicate any item.
The destruction catalyst ring and its big brother the catalytic lens are both banned because they can wipe out huge areas of the world very quickly, and they bypass plugins so you can easily wipe somebody's protected house, or the admin-built city, and admins wouldn't be able to restore it or even have a record of who changed the blocks. Further, a player who isn't abusing it to grief can still very easily grab all the diamonds in a large area, robbing other players of the opportunity and forcing them to travel far from home to get any. Blocking right-click isn't enough, because both these items also work with alternate fire (default R), so their ownership is banned. Leaving them in the game for all players would result in a wrecked world, widespread build grief, and a serious diamond shortage (lots of complaints from new players). Many of the rings and dark matter / red matter tools fall into this category - they ignore anti grief, are free or cheap to use, can very quickly make a huge mess which can't be easily undone, and the jerk will get away with it as long as nobody saw him do it.
Weapons and Top Tier Armor
The abyssal helmet allows the player to press R to fire a lightning bolt at anything for free, even rapid fire. It can be used to kill players even when PvP is off, and kill animals which would otherwise be protected by anti-grief. Similarly, the power weapons are banned because their R abilities can harm players and protected animals even when PvP is off.
Note that the philosopher's stone is not banned, even though its R ability can turn any animal into a Mooshroom (hurtful to the economy), and can turn another player's animals into the wrong type of animal. It can't be reasonably ownership-banned, because it's the key ingredient in the most important block in Equivalent Exchange, the alchemy table. Its right-click ability could be used to grief another player's protected build, so that ability is disabled.
The energy collectors are banned because they turn light into energy, which can then be turned into almost anything the player wants (including diamonds and other non-renewable resources). With the right setup, a player can literally have a sandwich while diamonds magically fill up a chest in the game, with zero active effort on his part and at no cost (the energy comes from light emitted by glowstone). Basically, the player now has an infinite flow of diamonds that he doesn't have to work to maintain. Once a player has all the diamonds he wants and more, of course he will be happy to give them away, since they're worthless to him but valuable to others. Now your whole server economy is wrecked.
If you install this plugin on a server where you've already been playing with others, I recommend you put energy collectors in your "world ban" list to ensure any already placed are destroyed.
Red Matter Furnace
There's a duplication glitch in EE which allows a player to duplicate any item using this furnace.
UU Matter Recipes
UU matter is an ingredient for lots of otherwise non-renewable resources including diamonds, redstone, coal, and so on. Unfortunately, UU matter itself can be made from renewable resources like wind and sunlight. So SOME of the UU matter recipes are banned. Most of them are not, and in particular, it's still possible to craft the highest-level IndustrialCraft armor.
The mining laser behaves similarly to some of the EE power items. It simply destroys too much world too quickly, creating potential for disaster in a griefer's hands. Note that players can still mine quickly with the diamond drill, which is still very fast, but not banned.
Because UU matter can be made from infinite energy sources like wind, sunlight, and water, a player can generate infinite UU matter, which can then be crafted into ores, which players ordinarily have to work to locate and collect. To protect your economy, you should ban the crafting of ores to block this path. For your server economy to work, it must be based on something that's in limited supply, and in Minecraft, that's ore.
The explosives are NOT banned because they do respect anti grief rules, and the default for THIS plugin is to prevent block destruction from explosions above sea level. This means a player can't make a big, unsightly mess with these, but can still play with them underground for fun and to mine.
Turtles simply don't respect anti grief, and can both place and break blocks, making them a great griefer tool. Further, a very simple program can send a turtle off to wreck a large area while the griefer isn't even logged in to control it. Note that computers are NOT banned, so players can still have fun coding some gadgets for their builds.
BuildCraft and Other Bans
I'm not 100% sure which mods each of these comes from... :)
The frame motor is SO much fun to play with, but unfortunately, it's easy to use the frame motor to either push unwanted blocks into another player's protected area, or even steal blocks from another player's area.
The cannon ignores anti grief, allowing player the player to break blocks he doesn't have permission to change, similar to the EE power items.
Some crafting blocks (like the automatic crafting table) are banned because they can be used to work around the crafting bans, allowing players to craft banned items. These items would then be confiscated almost immediately, so that player would have wasted the ingredients used to make the item, which is very upsetting. So many crafting blocks are banned by default, so that players don't accidentally make banned items.