Metrosh because I'm not a monkey to misguided paladins i'll explain why you can't tank as efficiently as warriors.
Static hate values vs Damage hate
Warriors have an ability called "Sunder Armor" which increases their hate by massive amounts, this is a SET value meaning that no matter how much dmg it increases all the same, the only way paladins could keep up with ONE sunder (they stack 5 times.) is if they were in all out dps gear in which case the warrior sunders again and all the pallies aggro is gone.
Paladins have some of the lowest overall dps in the game, and their aggro holding abilities are based on damage not static values, also paladins don't have "snap aggro" meaning they can't taunt anything, so once the mob gets pulled it's gone.
warriors have massive amounts of damage mitigation due to might/wrath/dreadnaught. Once your defense skill hits around 430 (doable) you can't be crit anymore. Paladins dont have a snowball's chance in hell to ever hit this and warriors can only do it with full out Naxx loot.
as for using BoK as a reason to tank, thats a castable spell, everyone in your raid will have it.
Warriors also have no way of dumping aggro or losing it, therefore if you use a paladin to tank you'll end up nerfing down your raids DPS simply because the warriors will have to go VERY light on the damage. This isnt good as most end-game encounters have a maximum time limit meaning you'll need to go balls-to-the-wall DPS, something paladins will NEVER be able to hold aggro through.
Heres a good example of why damage aggro is bad.
For simplicity sake we'll say 1pt of dmg==1 point of hate
paladins hit for 600, with 108% threat increase giving you 648 hate, a mage pyroblasts the same target for 2800 (this is a low pyro too, by end-game standards)
That mage just instantly pulled with their opener and because you have no taunt the mob is now loose and attacking the raid, you'd have to do another 2300 damage or so just to get it back assuming NOBODY else in the guild was even attacking.
So hope this helps