If a group of highly armed combatants slaughtered elderly women and children in mass, and then he went after them to kill them all, I can guarantee I would have no problem with it and would expect innocent people to die and suffer as a result.
1200 Israelites were slaughtered. That is a huge number considering there are very few of them to begin with as they live in a small land, about the size of New Jersey.
This is a fight for their very survival. It is either fight, or jump into the ovens made in Iran.
The choice is their own, but if you ask me, it is not much of a choice, it is a duty.