In today’s (chronological) Bible reading… Leviticus 11-14… we see the idea of “clean” vs “unclean”, in the areas of food (ch.11), birth (ch.12), disease (ch.13,14), and normal body functions (ch.15).
These laws served a hygienic purpose, but a spiritual one also. As God’s people, Israel was to be separated from everything God called “unclean”. Other nations/people groups may have participated in such things, but God’s people did not.
One person’s sin would not just be his or her sin… it would spread to others and become the sin of the people.
As Christians, we do not live under the Law. But, we are still to discern between what is clean and unclean… what is Christ-like and what is not. It’s not so much about what is proper or not… or what is inappropriate or not; those things vary from one person’s opinion to another. It IS about what Jesus would do or not do, say or not say, think or not think.