Who cares? If they run ahead and start pulling just grab aggro and do your job and tank. People expect dungeons to be cleared quickly since they're not that difficult and it's exhausting having to run the same ones over and over.

I hate the "you pull it you tank it" mentality that some tanks have, it's more toxic than the non-tanks pulling. I'm not there to teach people a lesson because they're doing something I might not like, I'm there to get my tomestones as quickly as possible.