Accusing someone of supporting genocide should not be considered an appropriate way of asking them to provide a more considered, nuanced opinion.
And if you say that both sides have a lot of valid points and you aren't sure how to weigh all those points to reach a clean and simple conclusion? Well... I've never won any friends like that.
But to answer your more general question of who gets to decide "appropriate", that is society as a whole. We, as a society and as a civilization, decide what we find acceptable and objectionable. Right now we have drifted into a territory where a one or two sentence soundbite is considered appropriate to encapsulate complex issues that defy easy solutions despite the soundbite pundits, politicians, and activists that spout them as axiomatic truths, shutting down the ability to have a conversation with anyone who slightly disagrees.
Do you have more insight on this, on how it could be handled better? Or are you happy with the status quo where little conversation but much shouting is the norm?