My main was a tank for 6 years or so. I almost never had people pull ahead of me because they didn't have time to. The only person you should slow down for is the healer.
If they don't dps the right target or do whatever else they're supposed to, it just gives you the chance to get better at tanking in less-than-ideal circumstances. If they die on something that was ultimately their own fault, who cares? If they QQ in /instance, just /violin them or whatever. They'll probably quit after they are the only one dying repeatedly. If you get kicked, so what? Like you said, insta-queue.