I guess I was thinking of something in between a private conversation and a meeting. Things like chatting in a shared office (which I know is a distracting no-no in some contexts, but not all, at least when it comes to a slightly extended greeting/farewell), or in the kitchen/corridor/doorway/photocopier room. Anywhere people naturally gather and mingle when they're not necessarily in full work mode. Depending on the workplace, that sort of thing is very common and a ban would seem weird and draconian.

It really is easy enough in practice. As tech folks, I know we as a group naturally hunt for edge cases, but I can say with complete confidence that everywhere that I've worked that put the kibosh on politics/personal during everyday business discussion was a much more humane place, for everyone, to work than one where such limitations weren't present.

I disagree that those are edge cases, but I'm happy to accept that we've had different experiences.