I'm with #43 - if everyone else started dressing UP, perhaps this might be much more helpful - I know that suits are uncomfortable, but not as much as being dead from a terrorist attack! Make it "an adventure in clothing statements" "BE ALL DRESSED UP AS YOU CAN BE" (new FR slogan as opposed to the old military slogan)
Americans have a constitutional RIGHT to dress badly. Everyone knows that.
IMO, there is no excuse for showing up for a flight looking (and smelling) like you just took a break from cleaning out the garage or mowing the lawn. Once a few years ago while waiting to check in for a five hour flight, the fellow in front of me was informed "Sir, you can't fly in First Class dressed like that." The man, who looked to be in his mid thirties, was wearing what appeared to be his high school football practice jersey, one of those see-through mesh affairs with large numbers on it, baggy, knee length basketball shorts and rubber slippers, topped off with an adjustable mesh back baseball cap, then proceeded to explain how important he was (Vice president of some company or other)and how he was entitled to dress however he pleased. "Not in the First Class cabin sir." Bravo! I say. unforthunately, I don't believe they still enforce that policy.
Requiring business suits may be going overboard but there should be some limits. Personally, I prefer to travel (And I travel a lot. On the order of 50K to 100K miles per year) dressed in slacks or chinos, sport shirt and sport coat. I wear the jacket because You never know what the weather will be like at your destination and you never know when your flight to Honolulu will be grounded in Chicago for 48 hours or more while your luggage goes on ahead. I have learned from experience that I get more cooperation, and far better service when I am well dressed than when I wear jeans and sneakers.