Spam is unsolicited, and will keep coming no matter what you do.
Web ads are implicitly solicited. You go to websites knowing that they will serve ads. If you don't like it, you can stop going to said websites and no more ads.
Email spam is implicitly solicited. You open your email knowing people are sending you spam. If you don't like it, you can stop opening your email and no more spam.
Web ads are implicitly solicited. You go to websites knowing that they will serve ads. If you don't like it, you can stop going to said websites and no more ads.