The problem is that leaves you open to e.g. Car companies putting out ads that promote their gas guzzling cars while banning climate change ads that might warn of the consequences of using such vehicles.

If you do what Twitter is now doing[1], "restrict rather than outright ban", you're back to having to serve as an arbiter.

[1]https://www.theverge.com/2019/11/15/20966897/twitter-politic...