Social media and individualism result in increased isolation, as it tears apart the social fabric of our societies. For many there is not much interaction beyond the family circle. Even neighbours are just strangers. This ultimately will undoubtedly lead to major disruptions and social unrest. How do we go about breaking that cycle and build real communities again?
OP is talking about building communities. IRL interactions are situated in a context: a group of friends/neighbours/coworkers or an explicit community meeting.
When people are talking in that context, they think about the opinion of the rest of the group. Saying something unacceptable will burn bridges. Being impolite can do the same thing.
But interacting online typically doesn’t have that risk. We split off into our echo chambers and align with people who share our beliefs, so there isn’t a cost to saying something unacceptable.