Please explain what those differences are without using any magical thinking that places sex into a sacred sphere of human activity that is holy and sacrosanct?

Or don't. My point is you can tell how serious a person is when they start talking about the morality of sex by replacing every mention of sex in their point with "boxing". It's still a highly physical one-on-one activity that's a crime of both participants haven't consented, so if the exact same argument doesn't make sense when made about boxing then they are thinking magically about sex and not materialistically.