The reasons behind the great divide in current world Jewry.
The dismissive answer to this question is the one you'll most readily hear from Israel's supporters: "Those Jews are stupid!" The other diminutive answer is, "They're self-hating Jews!" I suppose there is a bit of entertainment value for some in giving such responses, but neither answers the question let alone gets to the heart of the matter as I will attempt to do here as succinctly as I can. By the way, calling an individual a self-hating Jew is an ethnic slur that I don't allow on my social media pages or posts. Intelligent people give more contemplative responses.
There are so many divisions and exceptions within Jewish thought, including on this subject, that I'm not sure where to even begin. In the interest of full disclosure, I'm a religious Jew who does not support Israel in this massacre (obviously, my word, not theirs). But I have Jewish friends who are secular and who also do not support Israel. This isn't as anarchist as it sounds. There are Holocaust survivors, former Israeli officials, current Israeli citizens, and IDF veterans who agree with us. Hundreds of thousands if not millions of them. So, let's divide this into two categories of objection to Israel's bombardment of Gaza. Religious and secular.
The secular objection to what Israel is doing is that it is excessive and therefore inhumane. Since everyone relevant to this subject in the Israeli government has admitted that in the end, this bombardment will not defeat Hamas, it raises a question: Why keep doing it, then? It would appear that some other agenda is afoot that can only be accomplished by creating this catastrophe. That appears to be, based on public statements by some of those same Israeli officials, genocide of the Palestinians, and the ethnic cleansing of Gaza. If proven, according to the articles of the Geneva Convention these would amount to an international crime for Israel and its allies. This has nothing to do with letting Hamas get away with the atrocities of murder, rape, arson, kidnapping, and torture. We have world policing organizations that are pretty good at catching the bad guys when we utilize them. The United States' CIA, Great Britain's MI6, the European Union's Interpol, and Israel's Mossad exist for such occasions. Working together in conjunction with other government agencies, Hamas would be brought to justice. But if Israel and its allies purposely choose to forgo the deployment of the very agencies that world leaders have created to bring terrorists, huntas, and despots to justice with the least amount of civilian casualties why then should secular Jews support this massacre? ...and that's exactly why they don't.
The religious objection to Israel is that our prophets foretold to us how G-d's government would be established in Eretz HaKodesh (the Holy Land) and what it would look like. And frankly, this iteration of Israel ain't it. Our prophets said we would be led back into the Land from the four corners of the Earth by the Messiah; G-d's anointed representative, and that he would govern us there. The transition is to be so peaceful that weapons of war ("swords", in the verse) will be recycled into farming tools ("beaten into plowshares"), and that no one will assault us (or "make us afraid"). Our prophets give us examples, such as "the lion shall lie down with the lamb," implying this same sentiment.
Religious Jews the world over such as myself, have clung to these and other prophecies for millennia. So, how did we get to where we are now? Enter, Theodore Herzl. He was an atheist, Ashkenazi Jew born in the 1800s who grew up witnessing and hearing about the constant mistreatment of his people, which eventually became to be known as antisemitism. He believed that the Jews would logically be safer if they lived in their own country filled with and protected by their people. As far as Herzl was concerned, any land would do as long as it was populated with and governed by Jews. Several nations and places were candidates for "Der Judenstaat," as he called it, meaning "The Jewish State." This is also the title Herzl gave to a pamphlet he published on the subject. Initially, the overwhelming majority of Jews balked at even the notion of such a thing. One man's vision superseding G-d's prophecies? It wasn't even to be thought of amongst the pious! Fast forward 50 years, add some artful rhetoric and political maneuvering by the United States and Great Britain with significant funding by the Rothschilds, and voila! Der Judenstaat became "Zionism," and Palestine became Israel. No Messiah required. Yet this government claims to represent all of the Jews of the world and to be the designated safe space for the Jewish people. We, the religious objectors, object.
Ultimately, if Israel is not led by G-d's Messiah and it is therefore not His nation, why then should we, the religious Jews support this massacre? ...and that's exactly why we don't.