I tanked a 5-man PuG the other day, Drak'Tharon I think it was - The mage having seen me chain pulling 2 packs of mobs decided to run ahead and pull a third pack with Arcane Missiles. I taunted the (four) mobs off him and got them under control, then said "Do that again, and you're tanking them - please let me pull as it helps me maintain control of the situation we're in". We got about halfway through the instance before he did it again, so sure enough he died and we cleaned up. We got a few more packs further on and he ran up and AoE'd a pack of four with Blizzard, and also pulled two patrols in with the bargain. I DI'd the healer and let the rest die. Fury Warrior complained so I said "Blame the mage, you saw me warn him" - Is it proper of a tank to allow his entire group to die just to prove a point and teach a lesson to an errant DPS?
Imo no, you let the person causing the problem die, but not the entire group. Hell I've done it before too, but that doesn't justify giving the 2 others repair bills. So yes you were right in letting the mage die(lol clothie repair bill), but no you weren't right in letting the warrior(oww plate repair) and other die as well.
I did offer to pay repairs once we'd finished the run, the third DPS was from guild so said it was fine, the warrior had left the group after loot was done and was cross-realm so I couldn't chase further. I dunno, I felt bad for doing it as I could have probably collected the lot of them up and cleaned up after the mage *again*(Pally tank after all), but I felt the lesson needed teaching.