Depends what you mean by 'wrong'. It's certainly a cognitive mistake to do so, pretty much by definition. If you embrace either optimism or pessimism, your view of the world is less likely to be veridical than if you abjure or correct for either.

If you mean 'wrong' as a value judgement, I'd agree it's arguably reasonable to opt-in to optimism or pessimism on non-cognitive grounds. You might prefer optimism if you believe an inaccurately sunny view of consequences is pragmatically effective. Or you might prefer pessimism if you think it leads to reduced disappointment.

What also follows is that, given their opting in to non-veridicality, us third parties should take the views of any self-proclaimed optimists or pessimists less seriously than we do those who take cognition seriously.