I'm a female runner who has also competed successfully in a completely unrelated sport. I'd agree with the premise of the OP. Whilst some runners are very nice, I have never encountered so many oddballs in one setting. Away from the sharp end of the race (I'm not elite but am good enough to sometimes win local 5 and 10ks), many women competitors behind me can be odd, confrontational and jealous. I once finished third in a 10k, and another female competitor, who had finished 3 minutes behind me (her usual performance) came up to me aggressively after the race, along with two of her friends who were even slower, to accuse me of starting too fast and getting in her way and brushing her with my elbows. She couldn't understand any perspective than her own. I think she was annoyed that I was there at all and she thought that if I didn't race locally, she would be getting placed and running faster. It was a very strange mindset which saw no real logic but one that was clearly shared by her friends.
Amongst the male runners, again there seem to be quite a high proportion of those with social problems, 2 who have ended up in jail and another 3 who have narrowly avoided it, a couple who have committed civil fraud, a couple of stalkers and religious converts, and generally rather a lot of people who kind of struggle on the fringes of society in some way. A lot of them do seem to be either single or married or dating women from The Fillipines/Thailand. Of course, again, there are some very nice people.
Compared to my other sport, which is friendly, supportive, social and full of mainly quite mentally robust people, the issues with runners are put into more of a clear perspective.
One more thing that the runners seem to have in common (again with exceptions) is that they are all rather political but always very liberal and woke with little sense of humor and taking anything posted online too seriously. Very intolerant towards alternative not very radical opinions and any female who seems more successful than them professionally or in business as well as in running.
A couple of years ago, I started training with a group on the track even though I race mainly on the roads, and they are much better, supportive, encouraging and calm.