I've been a healer for 15+ years. I've been told how terrible I am by every DPS ever.

q: "why didn't you heal me?"

a:
- tank needed heals more
- you were standing in (fire, poison, gas, explosion ect)
- You ran out of LoS, your problem
- Did you even use a pot/bandage/cooldown to save yourself, probably not
- did you follow the fight mechanics? Probably not because you were 1 shot
- I had to choose between you and the other DPS guy, I like him more than you.

I'm not perfect, I try to be, but healing isn't a set rotation for optimum performance on a single target. healing is more of an art.. one that can guess the future damage and hope to get it right, or atleast correct for it before someone eats dirt. We'd like to see everyone survive, but if they die.. oh well.
Tanks get the same BS, just a different pile, and people wonder why tanks and heals are scarce. We put up with 100 times the crap the DPS does.