I would think it common knowledge by the majority of the fanbase that Tanks traditionally carry shields. The reason for this being that it increases damage mitigation.
The popular argument is that Tanks don’t “need” shields to effectively tank lower level (15-45) dungeons. This has to be players who’ve never been on the healer side of the field.
Simple math: Damage = Healer mana cost, hence, less damage = more mana available to the Healer for when it’s really needed.
Just use a shield, guys. You may think that just because you reach the end of the dungeon that everything’s great, but it can really leave a bad taste in everyone’s mouth when the dungeon run has to stop every other pull for a Healer to drink.
Just use the damn shield.