I had a t-shirt made...

"Summoner. If I have hate, someone else f*cked up."

Seriously, though... In the vast majority of this game, either the DPS check is too tight to cater to sub-par tanks, or the content isn't dangerous enough to matter. Yes, I occasionally pull a couple stray adds off the tank in large trash pulls, but whatever turns to me dies too fast to really matter. Yes, random DF groups can pair top-notch DPS with scrub tanks who don't have a prayer of a chance holding hate. However, in that instance, the trash won't pose and serious threat to the over-geared DPS. If they die, it's because they stood in AoEs, in which case even holding hate on the trash won't fix their stupidity.

Otherwise, a decent tanks shouldn't have issues holding hate. If they do, they should probably take a look at themselves first before pointing fingers.