Phil,
Simply because you have personal knowledge of guests at a wedding turning up improperly attired doesn't mean that it is in any way misleading to say that there are rules, and to suggest that those rules should be followed. On the contrary, it would seem to positively underscore the need to explain to people "how things are supposed to be done".

I gather from your last remark that, as there are a fair number of "dinosaurs" who are members here at X Marks the Scot, and to quote your paraphrasing of Julius Marx, "I wouldn't want to be in any club that would have them as members", you are planning on leaving.