For kidnapping, killing and torturing civilians and even bragging about on social media? Sorry, mate this is a terrorist attack on par or even worse with Bataclan. There's is no "historic" justification for this unless you're a full blown neo nazi.
I know your whole thing is being a RW edgelord, but read the fucking sentence please. It literally says "unjustifiable". That's why it's a -nuanced- position.
I'll try to dumb it down so you can understand
Murdering civilians at music festival == unjustifiable
Responsibility for the historical conditions that lead to the infinite bitterness driving that murder /= justification
E.g. it's possible to say "Israel has done many, many terrible and unjust things to Palestinians, including the killing of many civilians. However, none of that can justify this atrocity."
Further, you can say that the violence would almost certainly be massively decreased by a just deal for Palestinians. Hamas specifically thrives on Israeli oppression.
Finally, you can say that this atrocity does not justify the many, many Palestinian civilians who are about to die in the massive reprisal.
You understand how that works now? Nuance? Or do I need to dumb it down more?