Oh, really?
I feel your pain, and I dress, for the most part in a manner that you would probably consider appropriate to a given occasion.
However, some norms really are culturally derived and it is not so much a question of morality. Historically, distinctions in dress tend to reflect, not morality, but class differences. So you might argue that what we are seeing is a reflection of the leveling of class that is taking place in our culture, for good or ill.
But to say that it is declining morality, that really is a bit of a reach.
Oh, really?
The trend toward excessively casual clothing does reflect a declining morality because so often "casual" equals "deliberately revealing." When women are bouncing around with no bras, nipples sticking up, when skirts are so short that a crotch shot is likely, when shorts are so short that the lower half of one's butt hangs down, when men wear bike shorts so tight that one can see their religion, this is not just casual, relaxed clothing; this is a deliberate effort to display one's sexual equipment. And that is definitely due to a declining morality. It's hard to argue that a woman who is walking around on the street or in church with her breasts falling out of an insubstantial top or a man with his shirt off inappropriately is being moral in that environment.
“Historically, distinctions in dress tend to reflect, not morality, but class differences.”
For example, during the Middle Ages in Europe, the nobility railed against the lower classes wearing certain clothes and fabric colors reserved by law for the noble class. Curly shoes were a particular scourge.
We see the same distinctions in Mandarin China where certain hats and clothing denoted your rank and job in society.