Here is what I do as a healer

I let the tank decide the pace, if i don't like it, I ask them if they feel comfortable enough to pull more. If they reply angry I kick them, if they say they don't feel comfortable I try to encourage them to try and it's fine if they fail, atleast they learn (I remember a DRK once who didn't have dps stance on and was scared of his mana running out, i taught him what I could and he was very grateful for having learned something). If they don't want to try, that's fine too.

If a dps intentionally pulls more, either without asking or after a "no I won't pull more" from the tank I don't heal them and usually the tank doesn't take aggro off them either. If they do it again after being told not to, I vote to kick.

If a tank doesn't keep aggro not because they're new, but because they decided to pull mobs in dps stance and not use cooldowns, I stop healing them and take care of the mobs that are on me. (ofc after reminding them of tank stance and cooldowns and if they get angry..well..bye)