That's a lot of assumptions there. There are many reasons to believe that Israel has no right to exist that aren't connected to bigotry or racism. You could say a state of a single religion in power in detriment of other religions and peoples is a recipe for disaster, as it invariably disenfranchises part of what a real, non curated (read, oppressed/victim of genocide) population is, since there is no place in the world with open borders in which there is only one religion, unless enforced somehow. You could say other religions are allowed to exist in Israel, but we all know they don't get the same rights as those of the jewish faith or even safety.

The homeland of Jews is the same homeland of Christians or Muslims or Buddhists. A free, democratic, secular land is home of us all. My homeland is home for Jews if they so wish it. To create special bubbles for religions, such as a country for a single religion, is antithetical to democracy, freedom of religion and secularism. It's simply backwards thinking. Those are the values of the culture of a great deal of people and it's only normal they reject the antithesis of those values. Sure, there are many countries with primacy for a single religion, and their system is, imo, not any more right than what Israel is.

Then, you have the way of how that land was appropriated and how it continues to be appropriated. There is no plan in the near or medium future for Israel that does not involve mass murder and repossession. To accept the existence of Israel is to accept their current ethos. There were decades of chances and proposals for a two state solution or a one state secular solution, but they didn't happen and they aren't happening, so for many the question boils down to, are you ok with wholesale genocide of the Palestinians in order for Israel to exist ? Because as of this current moment, one thing explicitly implies the other. Not per se, but taking into account the entire history of the modern state of Israel and the plans of its current administration.

I think thinking this way is dismissing an entire swath of legitimate expressions of political opinions that aren't necessarily motivated by hatred of a religion or a race of people. I find it perfectly legitimate to consider Zionism and Israel toxic colonialist ideologies that have not brought and will never bring anything good to the world, but really, it depends on the context of before and after.

I could also consider that any person who thinks Israel has a right to exist is also expressing racism towards Palestinians, since for Israel to exist with their current plans, Palestinians must become stateless or be killed. However, i understand this issue is more complicated than that, since there are a myriad of reasons why someone could be thinking that. For instance, they could be thinking of a possible future where Israeli magically become human and stop indiscriminately murdering civilians, most of which children, then out of the goodness of their hearts spare an economically viable continuous stretch of land where Palestinians can exist in peace and make it illegal for wild settlers to drive them away from it. Like my dear, lovable and gullible EU does. For me personally I'd probably even disregard how much i idealogically disagree with the entire concept of Zionism, if genocide was off the table. I have the heart to try and accept other cultures, flawed as i may find them, but genocide i cannot.

Anyway, long story short, despite being used by antisemites, rejecting Israel or Zionism in itself is not evidence enough for racism or antisemitism and my opinion is that attempts of doing so are merely tools to groom public discourse away from the real problem of the ongoing genocide. Don't take my word for it, hear the thousands of jews worldwide who came out to express just this feeling.