The collision of two ideas.
Don't be a stupid jerk and refuse to serve people at a restaurant because you suspect you disagree with them, even if they are behaving politely.
The Internet is an extremely intolerant place. It is quite common for people to make snap judgments based upon minimal information and with next to no consideration that there may be alternate viewpoints.
I think you just touched on a significant factor, mentioning the Internet. A generation ago, the only way people interacted and learned the skills and courtesies required was face to face in actual conversations and exchanges, that had immediate consequences, we could see and feel. There were telephones and writing, but they were limited and minor; people had to acquire nuanced skills at communicating, and did, given the rich environment of faces, expressions, tones and attitudes in a wide population of individuals and groups.
But along came the Instant Internet with all its infinite attractions and availability everywhere. From that time on, face-to-face had a seriously seductive competitor, that could and did become as important or more important to many people. And by now there's a whole generation who have never known a world, or inter-personal communication without it. And on the Internet you don't get to see how that one unimportant word you just uttered before you getting to your main point just shut down all sympathy on the other side of the conversation. The thought doesn't even occur, until you're blasted by the flaming response, and then your Nuclear Defence Fail-Safe kicks in, when a mid-sentence "Whoops, shoulda said ___. Sorry.", sparked by their eye-narrowing could have saved the discussion and the friendship. Or the orders from the table of four.
We will eventually learn thicker psychic skins, and the skills this Brave New World demands, so we can smooth our brilliant insights into it without increasing the friction, but as with all human learning, it will come too little, too late, and for some, with overmuch bloodshed.
And I can't help thinking of a guy doing world politics by a couple of hundred thumbstrokes in the wee hours, while the dye sets.