I'd agree that ads can be useful for some things. However many major online platforms are flooded with scams to the extent that ads for anything that aren't obvious scams are suspect.

Also there is the converse proposition that: "all clicks are click fraud", that is, many web sites try to trick you into clicking on ads by making pop-ups that are hard to close, by making the layout shift so you click on an ad when you were trying to click a link, etc.