The purpose of a rule is not to teach people human decency, that is well outside our scope. It's to mitigate the impact those bad apples can have on others. Sure, a blacklist will help perhaps...but having rules that are so easily abused is a welcome invitation for trolls and a big reason why they are such a problem.
You give people too much credit. Of course we should all have human decency. But that simply is not reality.
Update: just beat a slow-roller. Took me over 2 hours. Said they were slow rolling because I got lucky drawing chapel with estates. Do we really expect someone that deranged to know that what they're doing is against the rules when it's not explicitly said so? And the game makes no effort to prevent it?