I would argue that for any given couple, inexperience will be a given, regardless of previous relationships, because they’ll be at square one on how each party’s unique qualities interlock. (Although that gets me genuinely confused as to the point of casual sex; what happened to the ideal of monosexuality?) So, there isn’t any intrinsic sanctity breach. And that’s not counting the situation of the widowed.
Note, by the way, that peasants et al. had/have many children as a failsafe against early mortality, not for anything the Duggars and Quiverfull would see as a purpose for such. (And someone tell Jim Bob that the quiver was for a recurve bow, not a repeating crossbow...) When people are confident that early mortality won’t be an issue and have access to birth control, they generally don’t have as many children. So don’t think higher-class reproduction wisdom can’t be applied by anyone else.