So to begin with there are obvious problems with viewing these foundation myths through the lens of contemporary morality (especially sexual morality, which wouldn't begin to take its modern form in Europe until well after the introduction of Christianity). So remember what we may consider rather unpleasant, violent, and barbaric tales of the original Romans probably did not seem nearly as bad to the later Romans who wrote them down centuries later for us to read.

That having been said even some Romans in the later Republic commented on how these tales were somewhat problematic from a moral perspective (Cato himself had a hard time reconciling Rome’s origins with his own rigid morality). Indeed these myths are rather unique when stacked up to other cultural foundation myths in that they paint the Romans in a less than positive light.

So what do we make of them? Essentially there are two ways to look at this. One, the Romans simply liked to celebrate the fact that a rag tag group of criminals would rise up, conquer the known world, and bring civilization to all they encounter (a theme common in later Roman literature). These perverse myths go to show that despite their great wealth, the Romans should always remember where they started and how far they've come.

Another interesting perspective is that because of their rather blunt portrayal of the cities founders as criminals and miscreants, there must be some kernel of truth behind such myths. It seems unlikely that later Romans would promote such an inglorious origin unless they were to some degree true.

Due to the lack (read: complete absence) of primary sources from the era it is unlikely (baring some extraordinary archaeological find) that we will know for sure to what degree myths like the murder of Remus or the kidnapping of the Sabine women affected subsequent Roman culture or whether subsequent Romans influence how these myths were formulated. These later sources, from whom we know about these myths, may have been attempting to portray their ancestors in light of their own ideas about masculinity, violence and progress.

Follow up question, is there a potential confusion here with rape meaning both by modern definitions rape & fornication? Or are we sure here that rape in this context means non-consensual?

I recall hearing of one element present in Roman sexuality, being that they were very into the concepts of "givers" and "takers", and that the balance of this was more important than genders themselves, hence their surprising historical leniency towards homosexuality or even the relationships with children.

Does anybody have any resources on this, or more information?