It's actually not that many, unless you're including those who are a bit apathetic or don't have strong opinions about Israel. They look bigger because they tend to be very vocal and are given disproportionate media attention, but honestly most Jews do not hate Israel.
Now, there are generally two different kinds of anti-Israel Jew here in the States: The fringe ultra-Orthodox and the usually young far-left social justice types.
The ultra-Orthodox who disagree with Israel essentially have theological arguments about how Israel was revived. Basically, some interpret texts in a way where they'll not accept Israel unless it's blatantly given to them by G-d. This is not agreed upon by most Jewish sects, even though it is canon to all of them that Israel should be reestablished (even with the anti-Israel crowd). It should be noted that these Jews tend to be insular and do not make up a large percentage of total Jewry. They're just given disproportionate amount of attention, and that's obvious when you look at how much attention is given to Neturei Karta (particularly by anti-Israel media outlets) despite being at most a few thousand. It's ridiculous, but a lot of people's idea of "good Jews" is limited by a small group of about fifty who allow themselves to be tokens to some rather vile anti-Israel (and quite frankly anti-Semitic) groups.
With the other group, I find they tend to be impressionable and/or far-left Jews who are obsessed about showing how "woke" they are. They tend to also be VERY far removed from their Jewish identity, whether that be their religious or ethnic identity (as "Jew" can describe both), so they view the situation from an outsider's view rather than one that seems to be more knowledgeable of the conflict. They buy into the Americanized racial view, where they apply white vs. colored dynamics and see the Israelis as totally white (many not even knowing what a Mizrahi Jew is, or the fact that no Jew is "white" by white supremacist standards) and thus "problematic". Their worldview of Israel is usually not based on anything that actually takes in Israeli concerns or fears, so they just see it as an awful state as dictated by propagandists they don't question.
I'm not sure I would agree with the idea that a Second Holocaust would've happened without Israel; however, I do agree that Israel absorbed many Jews residing elsewhere in the Middle East and gave them haven. Many argue that the "Jewish Naqba" wouldn't have happened without Israel; however, the fact that Christians are fleeing the area in massive numbers suggests otherwise, not to mention the staggering amounts of incidents that occurred prior to Israel's modern advent. It's quite easy to see where, without Israel, the Jews would've been in a worse situation.
I'll disagree that criticism of Israel means hatred of Israel and/or the Jews. I'll agree that many people's "criticism" isn't really valid and is just hate; however, I'm a staunch supporter of Israel, having family who lives there, and I have my criticisms of Israel. The thing is that I lay out my reasoning and show that it's not coming from a place of hate or bigotry. I have to say something because a lot of anti-Israel people are convinced that pro-Israel people do take literally all criticisms as anti-Semitic, when that really isn't the case.