So I'm going to chime in as a perpetual pessimist.
I've found tremendous utility in expecting negative outcomes. I'm wording this very pedantically, because my father and I used to argue past each other for hours re: "being negative vs saying something is negative."
Perhaps it's just that I've been in Ops/distributed system maintenance and development, but I've found expecting a worst case/pessimistic outcome pretty much always leaves me far more prepared, and more often than not, ends up being more predictive than my optimistic peers.
This has held true across time estimation, black box complexity, political outcomes, social overhead, model performance, outage frequency, pretty much every situation I can think of where I had to do long term planning in recent memory I feel well served by attacking from a "how is this going to go wrong/what are our blind spots/what do we do when this fails" angle.
The primary reason I make the (socially risky) statement of this is that I very often get (no hyperbole) guilted for being a pessimist, even when taking nontrivial effort for the negativity to be actionable and focused. It took me a good few decades to learn how to wrap my words and beat around the bush, (I was told by managers early on in my career things verbatim such as "you need to toe the party line more.") but even now that I experience almost none of the social friction that I used to, I find myself frustrated by the inefficiencies and gaps in this manner of communication, and find these gaps almost immediately ameliorated when I'm on teams which have a much more pragmatic approach towards being pessimistic.
Simply put, I had a very different experience than you, I've found an fixation on "being positive" to _massively_ impede Just Getting Things Done, and I've actually had much more luck bonding with coworkers over shared frustrations/issues and building lasting friendships like that than in teams where we're all wearing "let's be happy" masks. (This is a strawman, I don't expect you were arguing to this extreme, but I often find it manifests in this way in larger companies and as such want to try and argue the benefits of other angles of approach)