Honestly, it really depends on the situation and the level of content in question. As far as low level dungeons go the only reason there is to kick someone from the group is if they are going out of the way to sabotage the run for the other 4 people, given that a full BoE w/ enchants geared anything can solo low level dungeons, they'd have to be pushing pretty hard. This is my stance for just about any normal dungeon LFD group.
Heroics at launch are a bit different, but I'd actually take 5 minutes to talk to people or make a suggestion before pushing the button.
LFR? No idea, don't do it.
PUG Normal/Heroic raiding? The only time I'd kick someone that wasn't purposefully trying to sabotage the group is if they were intentionally spreading misinformation to get out of having to perform their role (tanks expecting the raid to move into inferno slice on Gruul so they don't have to move comes to mind, this actually happened), performing way under their ilvl (18k dps at 720?) or deliberately trolling the group (using Aspect of the Pack on Pounding or any other raid wide damage situation).
Mythic Raiding? I'd rather call the raid than deal with PUGs.