I think lots of players get rightly or wrongly blamed for a lot of things, regardless of role. I also think that considering how little the game does to actually teach the roles, most notably tanking, there's an expectation that everyone will either understand exactly what to do just from reading their tooltips, or go online to look up guides. Having such an expectation of new players is unrealistic - I think that assuming that all this basic play information should be available in-game is fair, and it's weird that it isn't.

Tanking in particular also seems to be hard for some people because of the responsibility. Tanxiety is a very real thing. The whole "pulling more than you're comfortable with" scenario could easily be avoided by simply saying "no, I'm not comfortable with that yet", but I've pretty much never seen someone say that. They just try it, and sometimes it works and sometimes it doesn't. That's part of learning, too, but every wipe is cause for angry chat messages.