Meta is probably the only large tech company where we would be better off if they had never existed. Or, at the very least, it nothing of value would be lost.
Or just social media in general. Even Mastodon is full of toxic people. There's probably something about social media style timelines that brings the worst out of people.
I think Twitter (and to a lesser degree its derivatives like bluesky, threads, etc) did far more harm than Facebook. It played a major part in ruining journalism and politics to a degree that far outshadows any other social media platform.
Twitter "ruined journalism" by giving lazy media companies a way to "track big stories" (i.e. a few thousand people comment about N and that's News, apparently.)
Facebook "ruined journalism" by virtue of users not bothering to read the news at all.
Both are horrible.
But, facts, "Journalism" was ruined by corporate interests decades ago.
FB marketplace is a terrible market. It does not allow exact searches. It forces scrolling hundreds of ads in the hope of finding what I need. Even Craigslist had (has?) far better searching. If you do something crazy like sort by distance half the ads disappear. It is full of scam ads (I have given up trying to buy used phones, for example). Sadly I am forced to use it because that is where all the local person-to-person selling happens.
In my area, it's basically replaced newspaper classified ads. So you get people selling cars, furniture, appliances, and miscellaneous stuff that's too big or heavy to ship. Except it's more restrictive, not allowing the sale of animals for instance, which is annoying.
My main problem with it is that it doesn't obey its own filters very well. If I search for "Buick" and set a radius of 40 miles from my location, it might give me a few within that radius but then start giving me a bunch from hundreds of miles away. And it doesn't seem to work outward, but might give me some 500 miles away and then one 50 miles lower down. That makes it less useful than it could be.
It's kind of like Craigslist, targeting local sellers wanting to get rid of things quickly rather than sellers wanting to ship things whereever the highest bidder might be.