> How can we approach these situations in a good manner and help those people with constructive feedback?

The same way we always have: mockery. Either they'll continue as they are or correct behavior. The lack of sensitivity towards dissonance might go against your wishes for "good manner", I disagree.

Something, something, participating in delusion.

A practical example: "managing upwards" by mocking the ideas, or more importantly/accurately: the outcome.