What exactly do you mean by groupthink? Let's taboo the word a bit:

• All members of group agree (same answer)
• All members of group have same/similar thought process (same process to answer)
• Answers or processes are flawed (this could just be a common mistake)
• Flaws are not corrected because group consensus is more important (this is the bit that distinguishes groupthink from a common mistake, it perpetuates)

Those last two are important parts of groupthink. Without that last one, mathematicians are guilty of groupthink, because they all apply the same (somtimes flawed) processes and get the same answers. Maths isn't groupthink because attempts are made to discover and fix flaws, and these attempts aren't ignored out of hand.

The kibitzer blocks out names and karma scores; so you can't tell what the group consensus is (either by the person's name; "the community thinks this guy is a troll" or by vote; "-5? this post must be bad"). I follow the same process as everyone else in evaluating a comment, but I don't know if I've gotten the same answer as them. In practice, when I've checked, I do get the same answer, so it satisfies the first two conditions. But is the process flawed? And is meeting the group's consensus more important than fixing these flaws?