What is bad about Zionism is not "uniquely" bad - in the post David links to I compare it to white nationalism and black separatism. I'm sure there are other such movements it could draw comparison to that aren't as immediately referable. What's bad about Zionism is what's bad about these other race-based nationalist ideas as well.
I find the notion of "the races work best when separate" to be wrongheaded, and efforts to enforce that idea to be repulsive. So racial separatism as a political philosophy isn't winning any points with me. And that is a core feature of Zionism, from its inception - Herzl railing that assimilation is impossible and Jews could only exist through separatism - to the modern era (those "scholars" warning that miscegenation will "make American Jews disappear".)
Further these notions attribute a nationality to a disparate spread of nationalities and ethnic groups, and then assert the need for them to have some national territory all their own. of course this presents a problem as this race-nation, by definition, lacks such an exclusive territory. To establish it, that territory must be taken from some other group. In Zionism's case, it was taken from the Arabs of Palestine. in White nationalism's case, it's been taken from a variety of people - and its continued rumblings keep talking about land-snatches from "lesser" people (lots of talk of establishing a white state in native-heavy South Dakota, not so much about establishing one in 99.99% white Iceland.)
"Lesser people" is also an important concept here. To establish this race-nation as such, the philosophy must insist upon the dfference form the people around its members. And of coruse theeasiest way to mark difference is in status. Andsince nobody wants to be lower status, the default is claiming that the race-nation is higher status. The nation of Islam insists that blacks are the special creation of god while white are pale imitations (hah hah) of the devil. White supremacism has a whole treasure trive of these sorts of ideas. Zionism actually lacked this in the early days, at least so obviously - the people already living in Palestine weren't considered lesser, they just weren't considered at all ("a land without a people" and all that) however it's since been readily adopted and incorporated into the philosophy.. perhaps because race-superiority is so easy and feels o rewarding to its adherents. it's like philosophical crack, and is just about as good for you.
And of course once established, the race-nation must remain pure. Else it stops being the race-nation, now doesn't it? if it has territory, it must be cleansed of "impurities" - whether those impurities are Indians, Arabs, Jews, Slavs, Armenians, or whoever. After all, not much use in having your race-nation territory if you're not the demographic majority (alternately you could use force of arms to subjugate the majority, as was done in South Africa, but that's a long-term expense and inherently unstable.) And of course the race-nation itself must keep "pure" by avoiding the out-groups. With Zionism we see these factors at work with the Nakba ethnic cleansing, all the way to modern concerns that mixed marriage will obliterate American Jews. We can see it elsewhere as in the railing against Spanish-language options here in the US, or just about anything the BNP says about immigration in your neck of the woods, plus the epithet "self-hating ________" or "race-traitor" used in pretty much every racist philosophy ever conceived.
And of course, there's the marriage of race and nation inherent to race-nationalism (like, duh.) if you criticize the race-nationalist philosophy, that must mean you hate that race - thus the SPLC becomes an anti-white organization according to white nationalists, anti-Zionists are derided as Jew-haters by Zionism, and if you have unkind things to say about Black separatism, you want to destroy the black race. This of course carries an inherent and internal element of self-racism, where members of the race are assumed to be "on board" with the philosophy, removing their individual self-determination... should they NOT be on board, they become disloyal, part of the enemy - "race traitors," "self-hating Jews," "Uncle toms."
The concept of enemies of the race-nation is important as well, and helps to bolster both the concepts of how the race-nation is separate and why "purity" is so tantamount. It's actually rather like how cults indoctrinate their members into believing everyone outside the cult is out to get them, as a means of isolating and entrapping the convert. When you believe that everyone in the out-groups is out to get you, any sort of fucked-up shit from the in-group is more acceptable because hey, at least they're family, right? it also serves as self0justification, "get them before they get us" in the case of violent movements. Further it's self-reinforcing, presenting the race-nation as a vulnerable cause to be defended from eradication - and it's always eradication, annihilation, and other apocalyptic fates. Apparently a race of people can only ever be wholly destroyed, never just jostled a bit. BUT REMEMBER WE'RE THE BEST AND STRONGEST EVER!!!!
These sort of ideologies are different from both standard nationalism and ethnic / cultural identity movements. The first is almost always an effort by the people of a territory to establish an independent state within that territory, usually of a pluralistic and equal nature - Scotland, for instance, will not be purging non-Scots from its territory, nor is it seeking to establish Scotland somewhere in Paraguay. The second recognizes human equality and differences within the group - chicano pride doesn't denigrate non-Mexican people nor does it claim that all Chicanos are of a unanimous and single voice and thought, the way race-nationalism does. There are of course sometimes exceptions, but they are not to be tolerated either, as they cross the rubric into racism and should be wholly opposed.
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