Not only tracking, ads can carry malware and viruses from malicious sites. They also can bog down the browser like Fandom wiki for example. Ads company are part of the problem since they don't screen them for malicious stuff.
I don't mind ads in general. I don't like it when they are in my face, lagging my mobile browser (Fandom wiki), demanding for notifications (redirector sites), autoplaying twitch stream (Fandom wiki), plastered the front page of search result (Google), and misleading games ads (mobile games).
I do have a few site that are whitelisted in uBlock because those site uses ads that are reasonable. Unfortunately, the rest of them are blocked because they can't keep it in moderation. I understand they need to make money to provides free contents, but that didn't mean they can use the ads like it is a wild wild West.