You can develop pessimism without a conscious choice, but once you become aware of how negative your outlook is, it's a conscious choice to not try to do better.

Being pessimistic about pessimism is individual-damaging and socially ruinous.

One can develop pessimism about pessimism without a conscious choice, but once you become aware of how negative your outlook on pessimism is, it's a conscious choice to not try to figure out the different meanings of that word and how important it is for the proper functioning of democracy.

Maybe read Orwell for a glimpse of mandatory optimism:

"The Ministry of Love was the really frightening one... Winston turned round abruptly. He had set his features into the expression of quiet optimism which it was advisable to wear when facing the telescreen.

with some it's an celebrated lifestyle: https://www.instagram.com/reel/DPCJpclgW04/

Indeed most choices we think we "make" are unconscious choices due to our environment. That does not mean we cannot introspect and learn and consciously change them.

I am much more pessimistic generally than I was 20 years ago. But that's something I work on, not something I accept passively as a fact of life.

Yes. It is mostly because of environment, and you can change your environment.