If you are ever asked this question, or any variation of it, by someone who supports Israel, do not dignify it with an answer.
It is nothing but an attempt to distract from the obvious fact that for the best part of a century the Palestinian people have been living under the boot of an oppressive apartheid regime that is guilty of crimes that far exceed anything Hamas could ever even dream of committing.
Do not give the zionist fucks an inch.
The denounce tactic is similar to red baiting where you accuse a center left politician of being a communist in order to cause them to attack communists and anyone left of liberalism. It's best to only respond by just calling it a stupid question and immediately moving on rather than taking the bait.