Most people would never consider putting into their mouth something that just came out of someone’s bottom, no matter how clean the bottom was supposed to be.
This is exactly why I have always refused to have sex without a condom, even when in a relationship. The thought of putting in my mouth something that was being rubbed against my intestines - or kissing someone who put in his mouth something that was inside his - just feels…gross? No matter how intimate I am with the other person.