In a way, yes. What is mature and professional behavior are decisions made by society. It's an opinion, but a consensus opinion of the society you participate in.

All manner of behavior - that you shouldn't steal, that you shouldn't lie, that you shouldn't wear your trucker hat to a business meeting - are all just the opinions of society. Some are made into legal contracts while the rest remain social contracts, but that doesn't mean they're any less important or valid.