Yet I understand that it's better for a tank to pull, cuz it's going to be simply easier for everyone, some people's attitude here is quite funny.
*Aw you pull I will let you die* - not gonna teach the puller anything, and if they are not alone, you can easily be removed from group simply cuz you didn't do you job at any time, especially before the last boss (that's not gonna feel good). If the group decides you should pull more, you should. If someone's struggling, yes, it's ok to take it slow.

I play a lot of healer lately and I've met different tanks. I get that some people don't learn fast, they need their time, but if you don't start learning now, then when? When you get to lvl 70 content and say you're new? Yes, you've never cleared this dungeon, but you know what a mob looks like and that you need to fight them and you have your defensive skills which for some reasons some tanks are afraid or too shy to use. The tank should know how to play his class by that time. If you're new to anything and don't know something, feel free to say that in chat and ask questions - maybe you have an experienced tank\dps\healer playing another role. How often does this happen? People just stay silent most of the time, then get surprised that group decided they will be better off without you.
No one is the leader in a group of randoms. The Entire group decides how big pulls should be.
Sooooo many problems could be solved so easily if people would just TALK instead of showing off their ass attitude.