(Tongue firmly in cheek)
Well, there IS the statistic that religiously conservative women are unable to orgasm... Surely that's got to color his worldview.
(Consider, all sex between minors is technically statutory rape, since neither can legally consent. Conservatism is most heavily conserved (heh) in isolated and tightly constrained environs (those most likely to produce incest)... And adult conservative women tend to be less gregarious with their sexual exploits. Perhaps the good senator is merely giving voice to a silently understood norm in more conservative culture?
)
/s
More seriously, the senator's argument is more in the vein of "there is compelling evidence that everyone alive today has pedigree that descends from a product of rape and or incest." While this is indisputably true (Neanderthals had such isolated populations that incest was abundantly common, at least as far as we can tell with surviving genetic samples, and unless you live in subsaharan africa, you are between 2 and 12% neanderthal), it is moot. The question begs the question in ways I am sure the senator does not really want. (There is a field of ethics that concerns itself with the consequences of potential future generations, rather than with the immediate consequences of living persons. This view makes murders especially problematic, as it deprives not only the individual murdered of their life, but also the lives of all persons that would have descended from them had they lived. When you take this into consideration, death penalties for capital offenses become very ethically dubious, and more conservative states like Texas just love their capital punishments.) It is moot, because it is impossible to predict the future in any such capacity, but we can predict and restrict the immediate harm caused by these practices. One is quite capable of acknowledging simple facts like this, without falling victim to the conceit that our outcome was the best one, or to courting the notion that existing populations should feel indebted to a known deleterious practice. The simple answer to his question is "Yes, there would have been people, they just would not be us. That would not necessarily be a bad thing."
There is also the possible (but unlikely) reality that the good senator is aware of the Toba Catastrophe theory.
https://en.wikipedia.org/wiki/Toba_catastrophe_theoryThe theory posits that human populations were curtailed to near extinction levels, which would have required incest for the human race to be around today, simply due to insufficient numbers of breeding members of the species.
However, this is still moot. We are not currently suffering from any such catastrophe; Human population is the largest it has ever been. The question still falls victim to the logical trap of being indebted to a known deleterious practice, as justification for permitting (or rather, enforcing the outcome) of that practice in modern times.
Really, the senator is looking for straws to support his position that all pregnancies need to come to term, and is not being especially critical of his own reasoning.