I would extend the "If two people agree on everything, then one of them is doing all the thinking" to "if members of a group of three or more all agree on everything, then none of them are thinking" - but then again I am about to give my Intro to Psych class a test on group dymanics and motivations... so perhaps I'm sensitized. But I do believe (dare I say - know?) that dissenters keep a group healthier than when the dissenters shut up and merely conform/comply/obey.

Next year I think I'll title this segment People Are Sheep and dare the class to come up with a valid and reliable counter-example! (Maybe send them here for research - who knows?)