Gear is the biggest factor. For example, you can't have a silly i310 tank in rabanastre who does his usual "one or two hate combos" at the start and try to cruise the whole fight in dps stance. It simply won't work that way! Simply put, if your gear's up to snuff for the tier and you know how to do big dps as a tank, you can rest assured your position as MT is secured even while out of tank stance.

If for whatever reason you lose hate after following the above, then the blame's just not on you. It's on the OT who sat in tank stance, or the healer who doesn't know how to avoid AoE overheal, or the stupid dps that are too lazy to use diversion. In either case, it's a win-win situation. You either get to be a dps-stance MT rockstar, or you get to yell at people's dumb mistakes.