I remember around 2020, a lot of freethinkers began spouting something about how Twitter is “a platform not a publisher” and therefore users are entitled to treat the website like a public meeting place and protected by first amendment rights, etc.

I think you’re taking that quote of mine with an unintended meaning. I didn’t mean to suggest advertisers have right to post what they want, rather they have the choice to NOT post if they don’t want to. The right-wing argument appears to suggest that advertisers should be powerless to choose or not choose to advertise. Suggesting they are wheat to be harvested. A resource owned by the company they are purchasing advertising from; its a bizarre notion.