Because it's usually right? See also: cynicism.
Reads article
Oh, this is about a very specific kind of pessimism in which a statement like "new economically-valuable technologies will emerge" is purely the domain of optimism.
Reads article
Oh, this is about a very specific kind of pessimism in which a statement like "new economically-valuable technologies will emerge" is purely the domain of optimism.
[EDIT]
OK, one example was a bit flippant and easy to dismiss, but:
"No, this isn't going to bring us meaningfully closer to economically-viable fusion power"
"No, this isn't the War to End All Wars"
"No, you're not going to keep your New Years fitness resolution"
"No, your company's not going to succeed"
"This miracle chemical's probably gonna turn out to be bad for our health. I look forward to finding out how fucked I am because of it in 40 years when someone gets around to doing anything about the alarming study someone will likely do in 10 years only to be ignored. If I make it that long. But at least we can make things fire-resistant 6% cheaper than before!"
Et c.
You're going to be able to breathe a minute from now.
Your whole life isn't going to fall apart.
etc.
There are unlimited hypotheticals you can make where an optimistic or pessimistic take is far more likely.
I can look at every amateur scientist who has found "a problem" with mainstream science, predict that they are a crank, and be right the overwhelming majority of the time.
I can look at every "breakthrough in battery technology," predict that it won't be on the market in 20 years, and be right the overwhelming majority of the time.
Nevertheless, there are YC applicants that found successful companies. Amateur scientists have contributed to scientific breakthroughs. Battery breakthroughs have made it from lab-to-market in much less than 20 years.
Appearing smart to dumb people isn't hard, so it doesn't count as a negative about pessimism :)
I won't make a judgement about it being usually right, but being pessimistic can be a tool to counteract the standard optimistic stance if you know people are usually optimistic (aka their expectations overshoot reality) on the subject