Systemd doesn't have to warn in the first place; that's a nice extra. But whatever it says, should be clear. The current message reads like systemd will blow up or silently kidnap your first-born when using a separate /usr. I admit that I was pleasantly surprised to be pointed to an explanation in the README. I also tried to avoid passing judgment. I simply observe that people are understandably ignorant about software they don't have an intimate relationship with. Said ignorant people should obviously not call developers idiots either.
I think I've now managed to piss off all participants in this thread. Sorry about that.