Well, because we are systematically persecuted even to this day by anti-Semitic people? Because 6 million Jews died only because they were Jews? Because Jewish homes have been marked with the star of David all over Europe since this war began? Because, as a Jewish Israeli, I don't feel safe to travel right now with everything going on in the world? Because a Jewish nation is how we self-determine?
Israel is the only place in the world where Kosher restaurants exist in abundance. Israel is the only place in the world where Orthodox Jews can peacefully observe the Jewish faith. Israel is the only place in the world where the streets are (mostly) silent on the Jewish Sabbath.
I also don't condone violence against innocent civilians. Yet, Never Again is now. If Israel does not respond with force, this will all blow over, and maybe in a couple of years, Hamas or the organization that succeeds them will try this again. We can never allow the massacre of 1500 Israelis (many of them not even Jewish) to pass like the wind.