https://www.nytimes.com/2021/05/13/opinion/ufos-aliens-space.html
One immediate effect, I suspect, would be a collapse in public trust. Decades of U.F.O. reports and conspiracies would take on a different cast. Governments would be seen as having withheld a profound truth from the public, whether or not they actually did. We already live in an age of conspiracy theories. Now the guardrails would truly shatter, because if U.F.O.s were real, despite decades of dismissals, who would remain trusted to say anything else was false? Certainly not the academics who’d laughed them off as nonsense, or the governments who would now be seen as liars.
I've seen a lot of people argue that UFO disclosure could be used as a distraction from other scandals. Most of Klein's post is in that vein as he starts to think about what the implications of extraterrestrials would mean for humanity. He does not push on what I think is the more interesting idea -- that a revelation that governments have been lying to us about about UFOs is a headline-grabbing way to get a lot of people to question official government pronouncements. If they've been lying to us about that, what else have they been lying to us about.
Note, alien life doesn't need to exist in this scenario. All that matters is public recognition of an issue where the government was shown to lie and people dismissed as conspiracy theorists were making true statements.
You know what will piss the world off far more than mere ufo disclosure? Is the Big Con about patents for energy and weapons and communications and parallel dimensions hidden from humanity for decades while people have suffered in lack and been robbed by their governments.