Well if you misunderstood, then did I.
Perfect example, I know a young lady in my family, that started dating in college, and whose family only found out she was having sex when she became pregnant. A common enough story, I suppose...
Well, this guy is no good.. She works full time while going to school, and he can't find any work at all, and complains about doing chores, or running to pay a bill here and there. He mistreats her, looks blatently at other women, and disappears all weekend.
Now, I can respect what you're saying about the concept of marriage not relying on state recognition. In fact, that's really why, to me, the entire "gay marriage" debate is pretty ridiculous. We are not in a theocracy, and all the state does is recognize a marriage, not sanctify it, anyway.
But I digress..
The average young people may not know what marriage even means. Now if you're restricting the scope of your message to those who DO understand the biblical concept of marriage, to saved Christians who nonetheless decided to go ahead and have sex, then I think there's more of a point there. They are probably more likely to understand what a big step they are taking, and in a LOT (I'm not saying "all" or even "most") they can be encouraged to marry.
But to say they've entered into a covenant, I've again got to disagree with that.
A covenant is binding, yes, but also VOLUNTARY. I would direct your attention to Exodus 24:3-7. The Israelites had a covenant with G-d, but they AGREED to enter into that covenant.
In fact, though it isn't biblical, Jewish lore holds that the Israelites were not the first people G-d approached to become the "chosen people." They were simply the first to agree to do all that G-d asked.