Explicitly denying a list of companies, e.g. Meta for now, is likely more legally defensible and gets around the issue of indie devs (who mayhap have TOS that allow ads, and it's the eye of the user that sees the ads, still patreon or straight up paid apps are more in keeping with the fediverse IMO). It also makes the point very specific that these assholes are unwelcome. Perhaps the EFF or someone could draft something... Trick would be to update it as new pricks enter the arena, but that doesn't seem unachievable.