What the heck happened to civil conversation even if you don't like what the other person says?

Was busy dropping facts about the current political situation (actual facts backed up with sources) and stated that I thought that the only way to correct current political corruption and overreach was to let the current administration continue to do what they're doing because a.) They're going to anyway and b.) people have short memories and yeah, no matter how you feel about Trump et al, they *are* abusing things - but then that much power shouldn't have been consolidated to just a few people. Been that way for decades... but anyway... Dude I've known for like 5 years comes back with general insults to my intelligence and threats to our friendship. In short, acting the exact polarizing way I was just pointing out among the more radical left and right. It was "instant REEE, just add water" reaction. First, if you're going on about someone's intelligence, it's probably because you have inadequacies in that department yourself. Most especially if the other person never brings that up. Second, don't ever threaten me because I'll follow through because *I'm going to take you at your word*. Our friendship must not have meant that much because that's what he was threatening. But, yeah, Imma take you at your word. Threaten to "beat me up" or kill me? Better knock me out with the first punch and, yeah, Imma come after you. Threaten to tell someone something about me to blackmail me? I'll tell them myself and not let you know so you can be seen as the evil moron you are. Things like that. So, yeah, no more conversing. Just "I hate you and everything you stand for and I don't like what you're saying so you can't say anything." And all he had to do was say something civil instead like "I don't want to have this conversation" or "I can't agree with you and I don't think we're going accomplish anything but an argument here" or something like that. I mean, geez, I'd have actually respected him for that. But as it stands, if I ever see him in town, he needs to pretend he doesn't know me. Where is all this stupidity coming from???