This is an interesting question.

I'm a Jewish person who has serious problems with Israel, but I immediately go on high alert if I hear someone criticising Israel. That's because there's generally 3 options there.

1. The person is not an antisemite, they just have real concerns.
2. The person is antisemitic and using Israel as a smokescreen to talk about the evil Jewish cabal (this is surprisingly common)
3. Some blend of antisemitism and genuine concern.

Now, if I don't know you, I have absolutely no idea which of the 3 you are. A common trait of antisemites is using very vague language and masking their true feelings. They know their view is considered disgusting by a lot of people, but also that it's also shared by a lot of people. Therefore they use 'test' questions to try and identify each other without stating outright. Israel is one of these test questions. People who are obsessed with Israel might be just really interested in foreign policy or they might be antisemites doing test questions.

About option 3, a lot of people have a tiny bit of antisemitism in them without realising, usually just from how they were raised. They might have what they think is a genuine conversation about Israel, but something will slip out that reveals the slight antisemitism.

Anyway hope that helps explain why Jewish people are sensitive about this topic.