Israel had a right to defend itself before it decided to flatten Gaza and kill everyone that lives there, as they're still likely to do. Once they decided to do that, they lost that right as they became the aggressor again. They only lost that title for about 1 day, anyway.
And of course, they've always been the aggressor in the West Bank and every Palestinian there would be 100% justified in killing any settler and/or IDF soldier taking aggressive action against their families and homes.
The part about Western/European guilt regarding the horrific mistreatment of Jews being mostly outsourced to Palestinians is a completely valid point, it's just not the whole story.
Germany, to use the most obvious example, is completely powerless (understandably, as there is obviously a ton of guilt there) to be critical of Israel for any reason whatsoever, even though public opinion there has long shifted against what they're doing in Gaza. The unimaginable amount of guilt from the atrocities committed by the Nazis very ironically prevents them from officially recognizing any position that is critical of Israel's actions, even though they effectively mirror the actions of the Nazis at this point.
It's just a pure hell world we're living in.