In terms of specific reasons to doubt the Gaza Health Ministry numbers specifically, I could go on forever about that, but I don't see the point of doing so on HN. It's not a tech-related question.
Regardless, our (USA) parties are in fact the biggest blockers to our functioning correctly as a liberal democracy. One is desperate for votes from anyone, the other party is terrified to pass anything or imagine any kind of future that isn't a slightly less grim version of what the republicans offer. Just by our ability to come to a consensus and do things as a country, we seem to have ground to a complete halt. So yea, people should be a lot more critical of whether or not we're actually espousing the democratic ideals we claim.
I do not agree with Israel's policies on the West Bank, but the issue is more complicated than I suspect you think and I encourage you to read Israeli perspectives on it.
B) Apartheid South Africa used the same excuse. That black people lived in independent bantustans who were self governing and therefor not apart of South Africa.
C) You are ignoring the fact that Israel very much controls Gaza, including every border crossing, the airspace and sea access, imposes a blockade, controls the registry, etc. Unlike apartheid South Africa, Israel does not recognize independent Palestine, let alone independent Gaza.