I have a friend who is a good person overall but really buys into the "real life is becoming Idiocracy" bit. I was frustrated, because I'm not the best real-time arguer so I don't think I did a good job of expressing why the movie is disgusting trash.
I attempted to talk about how it blames people instead of systems, and how it's an awful eugenics narrative. But we quickly got into a rabbit hole about whether intelligence can be passed on genetically or not and if that matters, and other dumb topics that went nowhere.
What's a concise and offline-compatible way of explaining why Idiocracy is bad & decent people should find it gross?
The problem is that you can't agree on Idiocracy if you both start from different premises, which seems to be the case. That's why you got onto different topics. Your big hurdle is trying to get enough common premises to start from so that you can both move on to the movie itself. There simply is no way to just say the movie has a bad message and your friend agree if they think some people are just naturally more stupid than others and think that the stupid people are the problem in the world. Ironically, that's a dumb person opinion. Not to be ablelist, but it's a very common idea with little critical thought or rigor.
A lot of people live with nothing but common sense. They're not curious people. They don't spend their spare time learning or reading things or trying to be critical of their own ideas. But through the general cultural filter they develop these ideas about the world and just hold onto them until they die. The idea that everyone around you is stupid and you're one of the few smart ones is exactly that kind of thinking. Idiocracy is a movie for that kind of person.
Plus it came out during a time of supreme liberal smugness about intelligence because Bush was a big dumb dumb poo poo head and they lost their shit over how someone so stupid could be president. All the hyperventilating about Trump's personality isn't anything new, they did it under Bush too. That was such a powerful cultural motivator for lib writers in the 00s.
You make a really good point about initial premise. I think you're right - that's the real disagreement, and I think it would be very difficult to convince someone that they're not fundamentally "the last smart or sane one" in a sea of dangerous idiots. It starts from empathy, and I don't know how to teach empathy. If teaching is even the right word.
Regarding your second paragraph, I agree, but I would add that it's very much a product of their environment. When you're surrounded by a a vast wasteland of inane garbage that encourages uncritical consumption, that's a natural result. I believe very strongly that people CAN be better, when afforded the opportunity. Including in areas like critical thinking.
In particular I think stand-up comedians makes this worse, which feature heavily in this person's life. Lines like "think about how dumb the average person is - then realize half of em are dumber than that" are funny, but also IMO make it easier to slip into this kind of framing.