Again and again over the course of their lifetime, a supporter of Israel is given the choice to either kill off a piece of their conscience or abandon their support for Israel. They are presented with this choice any time they see Palestinians being treated in a way they'd never want themselves or their loved ones to be treated?—?whether it's bombs, protesters shot by snipers, people being driven out of their homes, human rights organizations ruling one after the other that Israel is an apartheid state, tales of the racism and abuse suffered by Palestinians in the West Bank, or testimony about how horrific life in Gaza had been made for the people who live there, long before this latest round of killing began.
This information is unavoidable in modern times. You can avert your gaze, you can try to insulate yourself from it in an ideological echo chamber, but it will inevitably find its way into your field of perception once in a while. And every time you are confronted with it, you have to make a choice whether to compromise your personal sense of morality a bit further than it was already compromised, or abandon your support for Israel.