Unfortunately, it’s not a question of what’s rational.
My commute is on a busy B road where you have to properly cross the centre line in order to safely pass a cyclist. I ride sufficiently far out to make sure that even the chancers realise this, and in practice, the vast majority overtake safely and considerately.
You could probably get another cyclist to my left, but I bet that if you did, you’d get a torrent of abuse, despite the fact that it’s shorter and therefore easier overtake than two bikes line astern.
I occassionally cycle two abreast around town if I want to talk to someone I’m with (another luxury that apparently only cars are allowed) but only if the traffic’s light, and always singling out if there’s a danger of slowing other traffic down. I’ve still been hooted at by a car who had absolutely no difficulty overtaking anyway, and who we filtered straight past less than 10 seconds later as he joined the obvious queue in front of us.
People assume that riding two abreast is automatically inconsiderate, without actually thinking about whether it is or not.
The only solution is to get more people on bikes to see it from the other side…