However, Hamas is the government in power in Gaza while Kahane's Kach Party is banned in Israel because of its overt racism.

Yes, nevertheless, Hamas is not even all of the people in Gaza. It's only some of them. It would not be any more right to conflate all of the people in Gaza with Hamas than it would be to conflate all of the people in Israel with the terrorists who became the members of the Israeli government. People say that the Jewish terrorist groups disbanded after Israel became a state, and for some reason they think that just wipes the slate clean on the records of the people who committed acts of terrorism in those organizations. But the fact is, those people went on to become the government of Israel. So should we hold all Israelis responsible for their terrorist government? No, we shouldn't. That would be racist. As is holding all of the Palestinians in Gaza responsible for Hamas.