The problem with this kind of thinking is it goes against what a healer is in the party for, to replace health. By definition, a healer is there to compensate for the mistakes of others.
We cannot control the actions of others, and if their characters die, the healer is blamed, no matter how badly the damage dealer or tank was playing. The stress comes from this fact.
Now, ideally, players should own up to their own mistakes. But, that often is not the case.
People tend to overestimate their level of skill. It's far easier to blame the healer than for someone to admit they are just an average player who messed up a mechanic.