Maybe this is obvious to my three or four regular readers, but when I see the sort of discussions out there, and claims by high-level people who ought to know better, it occurs to me that people may get gaslit on this whole subject of what's allowed in war.
If you want catechesis in "just war" teaching and so forth, Here's the Catechism of the Catholic Church. It's all there. I'm pretty confident nothing I post here will contradict Church teaching; feel free to flag anything as confusing or poorly expressed.
Basic principle: people and nations have the right of self-defense. If someone makes war on you, you get to fight back. There are accumulated rules and norms regarding more civilized warfare, and while that notion may make you snort out your coffee, let's point out that if you toss out the rules, you get what Hamas did to Israelis on October 7: targeting non-combatants, torturing and raping, defiling and mutilating dead bodies, even infants. If there is to be war, then let us at least try to mitigate the evil. And since war in self-defense is morally justified, it stands to reason that can't be true if you can do anything once attacked. So mock the notion of just war all you want, but the alternative is worse. Why not have some guardrails to avoid worse?
So is Israel overreacting? Israel was attacked, so Israel gets to respond. Same as the U.S. (and NATO) decision to go into Afghanistan, because the U.S. was attacked from Afghanistan on 2001. Same with Japan after Pearl Harbor, and with Italy and Germany, who declared war when the U.S. declared war on Japan. Notice: no one said the U.S. had to wait till Germany or Italy attacked us; they declared they would, and so our response of a war declaration was entirely justified.
Israel gets to use its military power to destroy its enemies capacity to hurt Israel. Israel is obligated by the laws of war to avoid harming non-combatants and allow for the surrender of combatants and to obey still other laws and treaties regarding treatment of POWs. But in the main, Israel gets to make war on the force that made war on Israel, until the enemy surrenders or is destroyed. Blockades and seiges are tools of war.
It's worth pointing out that Israel goes to great lengths to avoid harming non-combatants. Even if you think they don't do it out of conscience, they have an equally strong motive to do it for reasons of politics and optics. No nation on earth can completely avoid harming civilians; the measure of morality in war is how hard you try. Some nations barely try at all. Israel tries harder than most, if not all.
Of course we hear the claims that Israel was unjust toward the Palestinians.* Let's just stipulate that it's pretty rare to have a history of two nations' interactions with each other, in which there is no injustice at all, or it's all on one side.
It's a complicated history, and a great part of the complication is that time and again, Israel's enemies weren't interested in finding any peaceful solution other than exterminating the "Zionists." Not an accusation; look it up. What you hear on American campuses right now is "From the river to the sea, Palestine will be free." That means, from the Jordan River, to the Mediterranean Sea, the territory will be Jew-free. That is the stated goal of Hamas and even more extreme elements who stand ready to kill any Palestinian leader who tries to seek peace. Thus Fatah, which rules the West Bank, vacilliates between talk of peace and extermination.
Those claims of injustice deserve a hearing, but they don't alter the basic calculus all that much. To put it another way: Hamas, the rulers of Gaza, had other means to redress those injustices (such as negotiations); they spurned them. Principles of Just War apply to Hamas, too.
At any rate, the news will feature death and destruction and sadness, but that's true of all war news. I cannot imagine how it was for my mother and grandmothers who listened, day by day, to war reports on the radio during World War II, especially with sons and grandsons serving overseas. But when faced with the task of winning war, resolve is essential. We wouldn't have appreciated being told, over and over, that we should back off of the Axis; why should Israel put up with such nagging?
* This term is more a political and ideological term than factual. Until the League of Nations validated the creation of territory called "Palestine" to be administered by the UK, circa 1922, no political entity or state of Palestine existed. As a geographic descriptor, the term goes back to Roman times and till the early 20th century, described a territory, not a nation. Of course these terms evolve; an example would be "Italy/Italian." The place Italy existed for ages; the political entity began in 1861. When people began to think of themselves as "Italian" versus other descriptors? Well, that's complicated.
Similarly, before 1922, the people who lived in Palestine were part of a succession of states, for a long time, the Ottoman Empire. Ethnically they came from many places, migration being a constant in human history, often encouraged by rulers, as happened in Palestine, which was often sparsely populated. They included Jews, Christians and Muslims, all of whom can point to a constant presence in the Holy Land. Quite a lot of the people of historic Palestine were nomadic -- e.g., Bedouins -- and moved about across political lines. What seems incontestable is that some number of families, tribes or clans have long-lasting roots in the area. The whole thing is complicated; don't let people mislead you by making it seem simple.