The pessimism is what comes after decades of optimism didn't work. And from decades of being on the receiving end of bad faith arguments engineered by oil industry propagandists, tested on focus groups for maximum impact, and disseminated among purportedly well-meaning optimists. Yeah, some people are gonna get snippy with you after dealing with that. And anyway, there comes a point when optimism is indistinguishable from delusion. The eternally optimistic make it a point of pride not to be convinced of anything that threatens their optimism, and thus their worldview. Convincing people like that feels about as achievable as trying to talk a devout religious person out of their religion.