We need to distinguish between moral responsibility and pragmatic liability. Innocent victims die in wars. All a belligerent can do - all international law requires it to do - is try not to kill any more civilians than the enemy makes it necessary to kill in order to achieve military objectives. Human shields may well be "innocent," but their deaths are the responsibility of the party that uses them as such, not the party that refuses to be deterred by their presence.
Any anti-Hamas Gazans who cannot escape the areas where Hamas has legitimate military targets are liable to be killed. It isn't their fault as individuals, but that does not mean that killing them is wrong, except to the extent that one says that Hamas killed them using Israeli weapons, a la "suicide by cop." That's why their blood is exclusively on Hamas's hands.
Killing human shields is tragic, and, indeed, traumatic for the people who do it, which is why dehumanizing them is inevitably part of the process. It's how those who must kill maintain their sanity. It is not ennobling, but it is how our species rolls.
From a cold anthropological perspective, one must ask why the Europeans were able to push the Arabs around. Why did Muslim countries not advance technologically as Europeans did? The Europeans were culturally "fitter" in a Darwinian sense, and nature selected for them. This is not a justification. It's an explanation of what happened, what has always happened.
Europeans did the same thing to the people they found in the Western Hemisphere and everywhere else. Hitler tried to do it in Europe, but the other Europeans were not nearly as far behind the Germans technically as the victims of European colonization had been behind the Europeans. So that didn't work out.
In short, as a cultural matter, the Palestinian Arabs did not know how to win, and they did not know how to lose. Their populations now consist largely of the thugs who run the place and the feckless masses who cannot figure out how to escape. That is a tragedy. But that does not mean that Israel should not do what it must to survive.
As far as "they elected Hamas," I have no problem thinking, because we elected Trump, that the USA may no longer deserve to be the big dog in world affairs. Take a less provocative problem like issuing the world's reserve currency. If the rest of the world gets in its mind that the dollar is not the best way to hold wealth, some very bad economic things will happen here. Those bad things will bring unhappiness to millions and millions of Americans who did not vote for Trump. Shall we say that the world owes it to those people not to abandon their currency over something a government elected by a majority of its voters did? Am I, a never-Trumper, responsible for the loss of our country's credibility on the world stage? Who do I see about not suffering whatever fate befalls the people living under that government on account of I didn't vote for it? The quantum leap from economic unpleasantness to dying as a human shield does not change the logic. I am not responsible, but I am liable.