But a paid licence will affect users that are all right abd for whom you're doing it.

I understand that using something with a risk of loosong access because you've upset the developer is something that will turn away a lot of people, but then again, I'd say that "don't be a dick" is a pretty reasonable requirement. The only issue I see that it's a pretty vague definiton, but maybe just limiting it to profanities and insult towards the contributors is something more concrete, which would be easy to fulfill and also enforce.