Oh, I have nothing against this rule either, but I do believe it needs to be explicitly stated rather than assumed. It should be publicly available for all to read on the website, not something you have to find out through email - or worse, by breaking the rule and being "told off".

While I'm not an expert on psychology, my observation is that if an adult is told off for doing something that they didn't know they weren't supposed to be doing, they tend to react negatively. The last time most adults have had to deal with apparently nonsensical rules was when they were small children and still learning how the world works. So a lot of otherwise sensible and mature adults will regress to infant behaviour if they're told off for breaking a rule they didn't know existed. Then you get the typically infantile whining and tantrums and "throwing the toys out of the pram" type things going on, and it becomes impossible to have a rational discussion with the offender. It seems to me that it's much more sensible to inform people of the rules in advance. Then, if someone does break the rule, you can come down on them like a ton of bricks and justifiably so.