The thing is, they didn't really raise good middle-class kids, in that my father ended up being a roofer and my mother a housewife.

You seem to have strange ideas about what constitutes "middle class".

Likewise, progressives tend to have this idea that having sex outside of marriage is a good way to make sure that sexual chemistry is compatible before marrying, plus it is just fun, and if protection is used and people are careful with each other's feelings, then there are no downsides

How about making it harder to bond with your spouse when you do settle down?