This is not a case for cruises out of NJ (Anthem, Oasis etc) or Baltimore, or maybe absolute majority does not dine in crocs. This is why I was surprised on Liberty 5 dayer to Bermuda recently.
Suggestion to change vacation is really clever although not called for.
Can you show me any documents Currently, for sailings in the Caribbean (possibly elsewhere), that's shorts and sandals (crocs).
If you do not have it ... and RCI website does not have this information, it is most likely that crew just does not want to have confrontations.