Dont get me wrong .Sure there is no excuse for a tank to not use his defensive toolkit. Especially since mitigating is part of the fun.

But is there any excuse for a healer who decides to troll the group on purpose?

The 2 other players did not sign to waste 45 minutes of their time in your personal crusade against bad tanks.

Grow up and help everybody finish the duty faster. Of course you should speak up and let the tank know that he is a problem and say something like:

"tank if you want to be an actual ... tank you will have to mitigate. You are not good at tanking and im compensating for this , because this team doesnt deserve to be penalized twice".