It's funny you say that the palestinians breed like animals. Yet that's the same phrase I've heard regarding the Jewish. “Be fruitful and multiply” is literally the first command/mitzvah of the Torah. A local Rabbi that I know has 10 children and he's in his early 30s! To which he believes he's faithfully upholding the commands.

I think all humans have same desire when it comes to breeding. I don't think the core instinct that made humans over such long period of time in evolution is going to particularly differ based on last few thousand years of separation. They will make more kids when they feel that the conditions seem favorable to have more kids, combined with the social constructs in which you are surrounded by. For example, during covid, birth rates declined because people were increasingly uncertain about the future. And even within Jewish subset, we can see that orthodox Jewish have nearly double the amount of kids versus non-orthodox. Use and availability of contraception also obviously plays a huge role, and if they were not available in the west, I think the west's population would be ever increasing as well.

Palestinians likely lack access to contraception, and therefore, will have higher rate of birth rate than Israelis who do have access to contraception.

So I do not quite agree with your original premise of why unification of the states is not a great forecast. But I still do agree that the idea of unification is pretty much screwed. There's far too much hate and strife between them at this point. I believe every such scenarios of the past ended in one way: extreme violence. If it ever gets to the stage of ethnic cleansing, certainly Israel will win with the overwhelming superiority in military power. But we're stuck despite that because the world is watching which prevents Israel from doing just that. We're at a unique impasse with no solutions.