When I saw one on Facebook I was insulted, because Facebook thinks I am the kind of person who is so stupid they believe in them. You can write this of as not actual harm because it is only emotions, but it had a negative impact on me, which I consider actual harm.
The other issue is information leakage. If you want to show an article on your phone to a buddy you don't want the ads to be for adult diapers.
For myself, I enjoy their failures. It's better to be wrongly identified.
And that ad for adult diapers alongside another for a plausibly deniable grape de-seeding utensil... More entropy FTW!