The main way I think about this and how I often see people act are that actions which undermine the long term success and sustainability open source community is abusive. So you take a behavior and say if a non-trivial number of people emulated/copied this behavior will the open source community survive long term, if the answer is no, then the behavior is abusive.

Of course people disagree with what will lead to long term sustainability of open source projects and communities, though it does seems like a reasonable heuristic to the first degree of approximation.

It's a spectrum IMHO from closed-source to "do whatever you want" source.