People who debate this often seem to argue for an all-or-nothing approach. I suspect the answer lies somewhere in the middle: be confident if you're a salesperson but not if you're a general, for instance.

I think a better conclusion is: be confident if you're being evaluated by other people, but cautious if you're being evaluated by reality.

A lot of the confusion here seems to be people with more epistemic than instrumental rationality having difficulty with the idea of deliberately deceiving other people.