Avery Are you not assuming that the parents have given them no guidance about going to far?
I think a large number of young people will give in to their hormones regardless of the quality of guidance they receive.
Sure, many will have the strength and character to resist, but why leave them alone with such temptation when we know that many will fall?
"Dating," where we just let a young couple go off alone, is older than most people currently living, but it's a pretty new thing. Chaperones only went out of style within the last hundred years or so.