What if an advertiser truly believes in their product and thinks it will better mankind? What if they've done a bunch of research into the product and theirs is actually the best on the market? I think the two are closer than you'd like to admit.
As a shoemaker, you might think your shoe is the best shoe on the market. Google doesn't care which is the best shoe. Google simply sells a product, namely, a credulous audience, to the shoemakers, who want buyers. And their ecosystem is bent toward improving that product. The shoemakers' noble ends don't justify the evil means of the advertisers.
This is kinda what I take the old adage to mean, "If you're not paying for the product, you are the product." You might think that Youtube, Facebook, Instagram, TikTok, etc. are free services because they don't cost you money. But that's like saying that a stay at the butcher's is free for the cow. They're not free at all; advertisers have to pay good money for access to their product, which is you.
Or so my view goes :) I could be wrong though.
Selling snake oil becomes no more socially good when the salesman deludes themself into believing the pitch.
The vast majority of products people buy help them solve problems of all kinds. An economic transaction is a win-win for both buyers and sellers. Look at products like the computer, the car, the telephone, etc. I think the world is becoming a better place as a result.