That's a crappy rule and it is incompatible with democracy. Part of the reason "freedom of expression" tenants exist is because voters need to be able to convince their peers on various issues. Religion is literally why people believe everything they believe in and asking people to avoid religious topics instead of discussing how to converse controversial topics without causing offense is precisely how you end up with social bubbles of extremes ready to tear apart society to destroy each other.

Part of that however is telling others explicitly when their topic of choice makes you uncomfortable and them ceasing the discussion after clarifying their intent immediately.

Same thing with politics, superpacs and millions in advertising money isn't how politicians should reach out to voters, it is supposed to be by voters talking to people on the other side about their guy and his/her policies. Civilized discourse about controversial topics is a corr foundation of a free society. And it is being eroded by modern social media driven society.

It also keeps a lot of encounters from uncomfortable or erupting. Fervent believers of different things, of course, are supposed to be converting the others, and being told that their god says your practice is heresy doesn't make the canapes taste any better.