The example sighted does clearly display the addage.. "you can't judge a book by it's cover."
BUT.. on a cruise ship the ambience of the ship and the cruise experience is created by more than just the decor. That's the purpose of the cruise line in having "suggested dress codes".
I don't believe it's exactly what the person is or isn't wearing which offends other passengers. It's the attitude of the passenger, that they'll dress how they choose because they can, with total disregard for anyone else on the ship.
In my view it's not those upset with what people are wearing who are the snobs. It's those who disregard the suggested dress code who are the snobs, showing total disrespect to their fellow passengers.
It would be simpler if the cruise line's enforced their own dress codes, but they don't want to offend a paying passenger... and that "opens the door" to those "those" snobs who take advantage.
No one has to show up in tuxedos and sequined gowns on formal night, but at the same time I don't image there are many people who don't have a sports coat & tie, and a nice cocktail dress in their closet.
You don't have to be rich to dress nicely with SO MANY clothing discount stores a couple can be dressed appropriately for $100.
On a cruise the old adage .... clothes make the man... also holds true. Not by how fancy or expensive the clothes are, but by the respect the act of dressing appropriately displays towards the other passengers.