The robustness principle is itself bad manners, in plenty of contexts. If I deliver packages by throwing them at the customer, I really want a customer to tell me "hey, don't throw packages at me!" before I attempt to lob something fragile and breakable, or something heavy at someone fragile and breakable. Otherwise, how am I supposed to learn that I'm doing anything wrong?

This is the point this has delved into internet crankery.