When there are unpatched browser vulnerabilities, attackers will use ad networks to inject attack code into reputable-but-ad-laden websites. And even when there aren't unpatched vulnerabilities out there, many ad networks will happily accept scam ads, ads that trick people into downloading malware, fake download buttons and suchlike.
Adblocking is an arms race. Google is handicapping adblocking progressively the fact that it doesn't take one day to achieve absolutely doesn't make it a myth. Adblocking is technically worse and the more locked down our environments are the easier it will be to kill or drastically reduce it.
If everyone had the same attitude this would probably already be the case.
When there are unpatched browser vulnerabilities, attackers will use ad networks to inject attack code into reputable-but-ad-laden websites. And even when there aren't unpatched vulnerabilities out there, many ad networks will happily accept scam ads, ads that trick people into downloading malware, fake download buttons and suchlike.