but I've only kicked 1 person from a party before and that was a low dps slayer.
Not "all" Lancers do this.
Seems to me that only one raging here is you, which is rather funny because you took time to stress that this has never happened to you personally (I'm guessing at least some of your instance runs were with lancers)
I've never kicked anyone out because I hate being party leader. Just tell me what to tank and I'll tank it, no questions asked.
I never kicked anyone, but alas, already met 2 Slayers and 1 Priest who did. There's no standardization for jerks mmkay? They play all classes and races.