Well I think sex IS different in this respect - it is the only time we cooperate with God in creating life! We are co-creators with Him, which is a big responsibility.
I agree with you, though, that mis-treating your body is a sin also, it is the temple of the Lord.
Where in the Bible does it say that a wife can't refuse sex? I know it ays that a husband and wife can abstain, mutually, for various reasons.
Man, if it says in the Bible I can't refuse him I'm not showing him that!!!