Again... I pray no one takes this as a "personal" attack... (I'm just trying to teach what we believe).... but we believe that sex should aim at a deeply personal unity, a unity that, beyond union in one flesh, leads to forming one heart and soul; it demands indissolubility and faithfulness in definitive mutual giving; and it is open to fertility. Without this aim, we believe any sex act (however beautiful, sensual, loving etc.) is LACKING. Our teaching is not about the negative -----> but instead really tries to teach that sex is BEAUTIFUL and AMAZING and God desires us to experience it only in the best way possible.... anything else is less than what could/should be.
I realize that the Catholic teaching is that marriage is a sacrament and therefore conveys grace, and therefore, in the Catholic context, it could be argued that a couple is materially changed in the course of the ceremony... but outside that belief, to me it doesn't seem like there's a lot of difference in either indissolubility or faithfulness of a couple from before to after the wedding.
The issue of fertility aside (since I hope you realize that many, if not most, faiths do not share the Catholic view on things like fertility and contraception), it seems to me that marriage is a declaration and an acknowledgement of the indissoluble and faithful nature of the relationship that was there long before the wedding. If the rationale for waiting comes from a requirement for that nature of the relationship, and not the wedding ceremony
per se, then I can't see where the objection would come from.
Now, I realize that I've set some issues aside (e.g. fertility and the sacramental nature of marriage) that are very important from the Catholic perspective, but I hope that you can see how people who don't share the Catholic view on
those issues can see premarital sex as not necessarily being out-of-keeping with the other view shared by Catholics and and many non-Catholics alike that sex is best saved for a loving, committed, permanent relationship.
If you see marriage as a declaration, not as a sacrament, then you logical conclusion would be that the couple has the same fundamental nature before and after the wedding.