You're right about the positives that could happen, and that occasionally do happen. The problem is what happens most of the time.

As you mentioned yourself, advertising is adversarial. It's a negative-sum game between competitors, and has a lot of nasty externalities. I have some more specific thoughts on this, and after posting them on HN many times, I eventually collected them in a blog article:

http://jacek.zlydach.pl/blog/2019-07-31-ads-as-cancer.html