That's not really true. When it comes to abstinence, there never really were a whole lot of adherents. People have been having sex before marriage since the country was founded. Before trustworthy birth control and abortion, the most common outcome was simply a wedding. During Revolutionary times,
30-40% of American women were pregnant when they married. As a result, "an inevitable lack of self-restraint," as you put it, absolutely is the superior argument.
If someone wants to argue that birth control is immoral, as the Catholic Church does, fine. They are free to do so. But pining for a mythical past during which good Americans had the common sense to keep their hands to themselves until they said their vows is just silly. That past never existed.[
The point here is that abortion was not a primary form of birth control in the past like it is today. I had a sister in law who got pregnant in HS. She had the baby and gave it up for adoption. Now we just get an abortion. That is dead wrong, pun intended.