Justin and Terrance are sitting in a cafe having an argument.
This is a serious argument with solidly intractable points of view. Let's say it's a "Black Lives Matter vs All Lives Matter" or a "Rape Culture vs Men's Right's" kind of argument. The two men might even get heated up, raising their voices, but probably not to the level of blatantly insulting one another and throwing glassware across the room, screaming "GO FUCK YOURSELF, YOU RACIST PIECE OF SHIT!" and squaring off for a physical confrontation that 95% of Americans are terrified of. In fact, while the two may disagree vehemently, there may be some points of compromise or simple acquiescence so that they can still enjoy the food.
Now position the same two men having the exact same argument with no food, on a stage, in front a thousand people.
The stakes have been substantially changed. There is social capital to lose or gain. The argument is no longer to convince one another of perspective but to win the approval of the crowd. Chances are, unless Justin and Terrance are feeling all Jerry Springer Show, there won't be over the top insults or screaming and likely no physical altercation but the argument is being viewed so it is at least part theater.
Finally, take this argument to Facebook (not Twitter because a full on argument generally requires more than 140 characters per response). The two men are no longer in the same location. There are the thousand observers who now get the opportunity to "like" points and even chime in. The insults fly with the ease of someone in no harm of punches thrown in the moment. In fact, because it's online, there seems to be little consequence unless one or the other manages to play the victim effectively and turn the online crowd's sentiments their way through emotional manipulation and gins up the crowd to join the insults and pejorative typing. This argument is ALL theater. And almost no one is going to change their perspective and only the most adult bow out of it.
Some folks use social media as a bludgeon, pumping up the discord and waiting to pounce on the unsuspecting. Best to avoid them as much as you can.
"The only winning move is not to play." -- Wargames (1983)