It's not I think that we don't suffer from confirmation bias - of course we do, and I doubt that we do properly compensate for it - it's that saying "groupthink" or "confirmation bias" without providing evidence doesn't advance the debate any, and seems to constitute no more than a way of sneering at people for not agreeing with you.

There seems too much discussion on this site regarding definitions. I call them "word arguments" and tend to skip them when I sense their presence. It seems people like to categorize things, in which case a word argument is an attempt to write dictionaries so everything make sense. I much prefer to try and understand what the other person is attempting to say, perhaps even without some specific, technical word to describe it, and continue the discussion in profitable directions.

In which case, the proper response to accusations of groupthink would be, "I disagree for reasons X and Y. Now to cover your other points..." Or, in my estimation, even better, "Why does it seem like groupthink to you?" You don't even have to ask them for their definition of the word to understand what they want to tell you, so long as they spell it out. And you don't necessarily have to answer the accusation of groupthink, then, either, especially if their stated reasons are not contained in the definition of the word. Instead, you answer the points themselves: what the person was trying to convey in the first place. And you might be able to suggest they use a better word or phrase, once you understand them.

Perhaps they are not trying to convince you that there is more bias than you think (which would require evidence), but just reminding you that it does exist and is probably not being adequately compensated for? If we agree that a problem exists, then we should welcome such reminders (at least until we find some other way to solve the problem).