Now. To be realistic—which is where we claim antinatalism comes from, yes?—there is ZERO likelihood that the species will ever go peacefully. (Short of social measures that would make people scream all kinds of bloody murder anyway.) I've heard antinatalists yellin' that our philosophy is going to save the world... no. I'm sorry. We may be right, but what does that matter? We're freaks. I don't mean that in the derogatory sense, I mean that in the sense that we don't happen very often. Most people are thoughtless and cruel. (Most of the time, when not making a conscious decision like this, I am too, out of instinct.)
Therefore, if people who are thoughtful enough to not breed keep on not doing so, and people who are thoughtless enough to keep poppin' 'em out continue to do as they are inclined, this will have a concrete effect on human evolution: if there's a genetic profile that leads one to susceptibility to antinatalist ideas, it will become scarcer and scarcer. The race will get crueler and more thoughtless. Life will be more swamped with unnecessary, human-created misery with each generation; if genocide or physical torture aren't constant, petty bureaucrats will be ten times as sadistic.
Therefore: Does the refusal of people who are inclined not to breed for moral reasons to buck their inclinations and reproduce their genetic stock in fact create more net suffering? I may pat myself on the back for keeping my unborn children safe where they belong, but I'm leaving the souls of my ilk in a position to be more and more nightmarishly outnumbered. So... maybe I should have a kid and then apologize to it? Or murder it if it's too unhappy? Can't come up with a good answer here, folks.
I'm afraid dysgenics is going to win. Even if I decided to let my own flesh and blood step into the meat grinder, on the average, getting people who are disinclined to inflict life to breed is no more realistic than the idea of getting people inclined to multiply mindlessly to knock it off. And although I agree in the abstract that overall suffering should be reduced, I could not stomach watching my own flesh and blood suffer through even a trial as mundane as junior high, especially knowing she'll be related to me, with all the nerdliness that entails—and knowing it was all my fault.
So, again, things are just going to get worse.
*If you're unfamiliar with this debate, Google "antinatalist."