His argument runs: without highly risky baby-making, his ancestors would not have been born
Wrong. The argument is twofold:
1) "High risk" procreation successfully produces viable families more often than not, and is therefore a useful strategy in maximizing reproductive success. The fact that those ancestors SUCCEEDED is evidence that their calculated risk actually paid off in the end, which leads us to:
2) Procreation IN AND OF ITSELF has an intrinsic moral value, for which statistical outcomes of that behavior
are not a factor. Whether procreation is morally praiseworthy or morally neutral -- or, in some cases morally objectionable -- depends on one's worldview, religious values or political theory.
These are two separate things, but you continue to conflate them as if they were the same. I'm saying that high risk reproduction is EFFECTIVE in producing families, and I'm saying that it is morally acceptable to the extent that REPRODUCTION ITSELF is morally acceptable. In this case, we have reproduction (an acceptable action) followed by concerted long-term efforts to preserve the health and safety of those offspring against sometimes impossible odds (a praiseworthy action) the combination of which produces a large number of descendants (a useful outcome).
Meanwhile, you cannot even claim to know what the probability of failure WAS, let alone demonstrate that any of our ancestors knew it, or COULD have known it, or even would have been expected to know it in the context of their own moral framework. The moral yardstick by which you are attempting to judge those actions
DOES NOT EVEN EXIST.
Where do you feel the point-by-point correspondence breaks down?
Same as I explained it: Rape is an action that is intrinsically immoral for reasons that have nothing to do with the risk of harm to the victim and/or any offspring that results from that action. That was one of the examples I pointed out to Angra, where I showed that rape would still be immoral even if the victim had no memory of the event and was not harmed in any way.
Reproduction, on the other hand, is not considered to be immoral, as it is the act of creating a human life. The moral dimension is defined by subsequent choices of the people in that child's life, including but not limited to the choices made by the child's parents. Bearing a child into a perilous situation is only immoral if you intend to allow that child to come to harm; if you do not, and believe yourself capable of carrying out your intentions, the situation is irrelevant.
Either both are valid inferences, or neither is.
Me:
Cars are fast
I want to get to work quickly
Therefore, I should drive my car to work
You:
Cable modems are fast
I want to get to work quickly
Therefore, I should drive a cable modem to work
Category error. Comparing normal reproduction to rape would imply that those two actions are morally equivalent; that one or the other is immoral
only under specific circumstances. And that simply isn't true.
Therefore I conclude that
1) High risk reproduction is
useful because (history shows) it has tended to work.
2) High risk reproduction is no more moral or immoral than low-risk reproduction.
Rape may be
useful for that aim too... but rape is unlike reproduction in that it cannot be justified morally. Because of that difference, your comparison is invalid.