Thank you for the wonderfully detailed reply :)
It's certainly worth considering that the internet may have a greater volume of content produced by crazy people. That doesn't ease my worries about a world full of people who are at least crazy at some low level sufficient to make them wrong about quite major stuff, but it does at least put my 'people are wrong on the internet?!' worries in better context.
If age alone is a heuristic of sanity, then things are looking quite bad because I think I'm one of the younger people who actively chats on the discord. But in general, I see what you mean and people are liable to change over time.
Regarding those who see their goal of kindness as an excuse to hate and persecute, that is certainly an issue. Binary two-party politics does tend to lead to a belief that anything you do is justified if it allows you to triumph over the truly evil, and that leads to no end of unpleasantness.
Regarding linking people essays and papers, unfortunately this doesn't tend to be received all too well. Norms-wise (in that community), it's generally seen as a bit rude to link people lengthy documents that the other person needs to read rather than providing a summary or argument as to why you personally believe the thing. That said, perhaps it would be worthwhile to do so anyway when I become frustrated with a conversation, rather than saying something rude or excusing myself and leaving without further debate.
On the meta perspective, changing the minds of these people is of course not going to change much about the real world. It's just something I enjoy doing, really. And perhaps if I cannot make myself enjoy doing it, then the solution is what I'm already in the process of doing: Not arguing with them.
I will consider this, at least, but it would sadden me to lose what I had once enjoyed.
This mentality is a good one. It's perhaps the high-level thing that used to guide me towards the behavior I'm looking to emulate but that I forgot to actively keep in my mind. A focus on understanding why people believe what they believe and a willingness to change my own mind may well have been the underlying positive trait that I have not been emulating in my present conversations. I will try to focus on this virtue and see if that improves things. Thank you.
I doubt a few minutes of pondering will provoke any significantly insightful thoughts, but on the off chance that they do here's what I've got:
A major pitfall of most tests is that they can end up examining a wide variety of confounding variables. For example if the test for rationality is based on a written prompt then it selects against those with dyslexia in spite of their rationality. If it's based on a spoken prompt then it selects for those with similar accents to the test-giver, or against those who had it read to them in a strange way. Ideally since the thing that we're selecting for is (I assume) practical reasoning skills, we would want the test to have some similarities to real life.
Thus the thought that comes to mind is an escape room which can be set up and run essentially-identically for each participant, whose puzzling elements require you to make Bayesian updates on multiple propositions that you were given an idea of the likelihood at the start. In order to avoid biasing the tests in favor of those with more general knowledge, the propositions would ideally be totally fictitious. It occurs to me that the elements of real-world pressure and communication would bias the test against those prone to anxiety, but given that that's a common problem when you're called on to apply your rationality skills in reality I think that may be an acceptable flaw, if no other options are obviously superior.