Actually, Luther taught that intercourse "is never without sin" but God excuses it. He was certainly far more advanced in his understanding of sexuality than his predecessors and their "traditional view", but he didn't advance all the way to accepting it as without sin or as being a gift from God. That really didn't occur until the modern age.

History shows that the view you are calling traditional is actually modern. If you subscribe to a view of sex as some form of spiritual bonding, then it's not only modern, it is post-modern.