Give me 1-2 examples of useful info we can get from ads?
For example, I found out about the local farmer's market in my city via advertisements being hung up around town, and that helped me get fresh produce and find some community. I'm not sure if I ever would have found that farmer's market otherwise.
I also found one job via a "Who's Hiring" hacker news post, and that's obviously an advertisement thread advertising open positions.
Of course, these do not balance out the negative impact of ads, such as advertising credit cards and sports gambling and gacha gambling games to get people into debt, advertising tv shows and movies to waste people's time watching garbage, and generally advertising garbage that makes people who were otherwise happy waste money and time for no real gain in life satisfaction.
I'd categorize job postings a bit differently, if Facebook was full of (legitimate) job postings I think it would be less of an issue. I agree on all the gambling stuff you wrote.
I think a lot of people use the term “ad” to refer solely to the latter category. This goes back to the origin of modern advertising (and even earlier with snake oil salesman and charlatans, which were scamming merchants using music and stage shows lol — sound familiar?) and using the term “public relations” as an alternative to “propaganda”.