Why do tourists visiting Italy have to wear certain clothes?

The simple solution is to wear a knee-length skirt or capris and to carry a wrap with you to cover your shoulders. You act like it's unusual, but most churches ask that shoulders be covered, whether they're Catholic or not. It is by no means the same thing as asking a Muslim woman to remove her headscarf in Westminster Abbey because you'd be asking her to violate her religion. Nobody's asking you to violate your beliefs, only to respect theirs. I don't enter a synagogue and when I visit a Buddhist temple, I take my shoes off. It's a matter of respect.