I would say right. I've thought about this topic a lot before (I actually remember debating this with my mother's boyfriend when I was about seven), would I kill Adolph Hitler if he was a baby. Every time, I've ultimately said no. There were many other things that caused Hitler to turn out the way he did. If he had made some different choices or some events had or hadn't occurred, then he probably would've lived a completely normal life. Perhaps extraordinary, but in a good way. He wasn't born a homicidal maniac, so I would kill him. Not until he physically harmed someone. After all, our lives can go in many different paths and I'm sure plenty of options could've taken Hitler to an accounting job or some such. Or perhaps he fought in the WWI and died. If it were me, I would probably just influence his life enough so that he wouldn't become evil. After all, even though he's Hitler, he was a boy and a human with feelings and emotions. I'm not just going to kill him mercilessly.
Not only that, but if Hitler didn't rise to power, Einstein wouldn't have come to the US. I think if Hitler didn't rise to power, someone else would have, when everyone had much more powerful weapons, and things would have turned out even worse.
Well, there was the "Baby Boom" due to the influx of returning soldiers from the war and then the amount of births greatly increased. Also, since it would be a completely different world if there was never a Holocaust, they're right. Most of US wouldn't exist, just a bunch of other people would be here instead (and I imagine the population would be significantly higher).
-_-