Not rude at all. The original question is why certain people behave in a certain way.

The first point addresses the direct reason why some voters would refuse to vote for Harris due to her stance on Israel. When people believe they are being harmed they tend to focus all their attention on the immediate harm. It's not a logical choice but people don't act logically in these circumstances.

As an example of this, I'd offer our response to 9/11. The entire nation came together to pass the PATRIOT act and start a war in Afghanistan. There's no logic in passing a bill that was so long that no one in congress could have read it before voting on it. It's hard to argue for the logic of invading Afghanistan. There wasn't really an objective (besides "get OBL", who we later ended up assassinating in an other country) and in retrospect it's certainly clear that it caused far more harm than good. But we were in an emotional state. The people watching their relatives getting bombed in Gaza are in a similarly emotional state.

The second point addresses why Democrats attempts to convince them are failing so spectacularly. Getting someone to vote for your preferred candidate is an exercise in persuasion. Much has been written about the art of persuasion and "insult your audience," isn't generally a recommended technique. One counterexample is "pickup artists". They theorize that by insulting or "negging" women they can motivate the woman to counter the insult by seeking the mans approval. While this does work on some small percentage of women, the vast majority are more motivated to find their mace.