The best argument against group-think is that it a bad way to make decisions if you want to reach the right answer, or at the very least, escape the wrong one. Let's assume one person offers to take action A, and 5 other people in the group offer to take action B. Assuming that decision A is right and B is wrong. If you use democratic decision making, i.e. go by the will of the majority, you take the wrong decision. Democracy would win, but the group would lose. The best option, in that case, would be to give the one person an opportunity to convince the rest that his offer is better. The biggest problem here would be that the majority may refuse to listen to his argument simply because they are the majority, and people tend to think the more people believe in an idea, the more true it is. Historical progress, however, was based on "truths" that were eventually disproved (proven to be nothing more than bad theories).