Okay I will answer the question differently. No I don't think Hamas does "lose the right to resist" because of Hamas killing civilians. But I still think killing civilians is wrong, and preferably war crimes (such as harming civilians) should have legal consequences, whether those crimes are committed by Israelis, or Palestinians, or anybody.

Edit: just to clarify, when it comes to "the right to resist", I don't think that includes the right to harm civilians. But if Hamas were to attack IDF infrastructure and try to push the IDF out of Palestine then I could see the case for that. If it's acceptable for Israel to use weapons to defend Israeli territory then it should be equally acceptable for Palestinians to use weapons to defend Palestinian territory.