I don't think you're wrong at all about the lines being blurred within American society, but this is effectively entirely the fault of how Zionism and the Israeli state has been portrayed to the American public by the government and mainstream media outlets for decades. There is almost a complete lack of education on the subject, by design, which leads to the average American to simply assume that Zionism and Judaism are the same thing, and therefore if you are anti-Zionist you must be antisemitic. On the flip side of that, if you are actually antisemitic, conflating the two is beneficial to you because you can simply use Zionism as a bludgeon to shit on Jews, or worse, commit acts of violence against them.
The general lack of public education on the subject also naturally leads to increases in levels of antisemitism across the board any time Israel does something fucked up and it gets reported on national TV.
I do think you are absolutely correct that there are some uniquely bad actors in the movement that present and use anti-Zionist rhetoric in a very insidious way.
With regard to my assertion that you're referring to here about Zionism effectively being equitable to Nazism, I feel like I should offer some clarification, even though I know it may be an unpopular opinion (though more and more people are seeing it for what it is every day). I consider Zionism, specifically as it is practiced by the Israeli government, to be functionally indistinguishable from the racist, genocidal/exterminationist practices of Nazism. I am not at all referring to the everyday Jewish person (or non-Jewish person, for that matter) who may or may not feel some type of positive way towards Israel or feels that a Jewish state should exist.
Pivoting to the question "Does Israel have the right to exist?" that has again surfaced in this thread: Let's be clear in stating that no nation has an inherent right to exist, and especially no nation that behaves the way Israel does has the right to exist as it currently does. Do I think that Israel should exist? Yes! I am 100% for Israel existing as a safe haven, not just for Jewish people, but for all people and all creeds. That being said, it simply cannot continue to exist as the ethno-nationalist, religious supremacist apartheid state that it currently is. Such a state cannot be sustained permanently, and it should not be allowed to. Their society has been spiraling for some time now, and collapse is inevitable. Thus far it is only postponed, not prevented, by the unconditional support it receives from the Western world.