For note that if unity and procreation really are inseparable, they're inseparable from both directions. Namely, if it is wrong to separate procreation from unity with the use of artificial contraception, it is equally wrong to separate procreation from unity and have offspring apart from the sexual act of the married couple. As a result, neither is acceptable from within official Catholic teaching. Let us again try to uncover the core of the teaching. The Catholic tradition sees marriage as both divinely instituted but also the most humanly compelling context for sexual expression.
Love puts down stakes.
Love reaches into the future. I do not truly love without truly committing my life and my future to my spouse's life and future. The fullest expression of love between man and woman finds its home in marriage, therefore. There is a more symbolic way in which to render this point. Things we have rights to are by this very fact no longer truly gifts.