Ah, confidence. I tend to do the opposite: I hedge too much. If I don't watch myself, I'd probably say, "I think 3 is a prime number...". Then again, I have been guilty of projecting confidence a bit too much, probably in a way unpleasant to others.

In some ways, just banning a particular behavior feels a bit too much like treating the symptom rather than the root cause. On the other hand, I can't imagine how to approach this problem more holistically.

More importantly, this rule is simple. Having a simple, strict rule like this will help people help themselves. If they actually want to be nicer—and, I've found, most people do—a few rules like this will help them catch their own bad habits. And over time, it will help them be more introspective. So perhaps it actually is a way to treat the underlying problem.

I've been trying something similar myself, pattern matching on some of my bad habits to try to reduce them. I don't know if it's been working holistically, but at least I feel like a nicer person. So that's something.