Calm down fumofu.
Healers who do let tanks have their bar on low life know what they are doing and will keep everyone alive.
When you have spend a lot of time healing in this game, you know how to analyze damages your tank is taking.
I'm part of those. None of my tanks has ever die. None have complain about it. Everything were always fine.
I however adjust. If I see the tank i'm running with not using defensive cooldown and take huge amount of damages, I sometimes won't dps at all.
