Well, far be it for me to argue with your grandmother. All I have are uninteresting studies and figures to offer in return. However, I do have a bridge to sell to anyone who believes that we didn’t see a rise in promiscuity as birth control became easier and easier to get.
Sorry, you’re just wrong. My parents were born in the early 20’s themselves, and my grandparents in the late 19th century. I have no illusions that people were virginal in those eras, but it wasn’t the steady stream of uninterrupted sex with multiple partners from the teens through the 20’s and often into the 30’s as it is today. Men and women still got married when pregnancy reared it’s head in those days, and that alone made all the difference in the world.
Ok, whatever you want to beleive is ok with me.