People say this often, but I don't understand how knowing about alien existence would collapse society. You announce aliens exist...then what? People still have to go to work the next day, eat, and so on. Unless the revelation is something along the lines that aliens treat us as livestock to eat and we can't do anything about it, or something similarly dark, I don't really get the purpose of keeping it a secret, unless the goal is to monopolize alien tech.
Personally, I think should aliens exist, they'd probably have some... uncomfortable opinions or facts for us at a bare minimum. I can understand the point that just admitting they exist isn't actively opening up a dialogue with extraterrestrials, but human curiosity would drive us to them. Ultimately, I think people would just get more retarded in a bad way.
Aside from that, I found Hal Puthoff's episode on Joe Rogan interesting. Even if you think he's a quack, his scenario for UAP disclosure is on-point.
The gist of it is, the Bush administration allegedly gathered several top thinkers, weirdos, and crack-pots to give their opinion on UAP disclosure and its resulting effects on American and global society. Apparently none of the groups had a positive outlook.
One top reason why disclosure is a bad idea is, supposedly, that several corporations would sue the government and several highly important MIC companies. If alien craft crash-landed, then the government scavenged the craft, and then gave that to specific companies for reverse-engineering, that's quid-pro-quo collusion. In-and-of-itself that would shake up American society in a big way. Moreover, it would have major effects on the status quo of
Pax Americana due to the possible bankruptcy of our top military providers.
Point being, there's no real benefit to revealing aliens, at least none that would outweigh the negatives.