You start by saying that Zionism used to seem to you “too much like a muted form of imperialism”. But you don’t say why you thought that…
Was it because you were aware of
* the European origins of Zionism;
* the backing it received from British imperialism from 1917 to 1947;
* the way Zionists massacred and expelled Palestinians from late 1947 through 1948;
* the way the IDF went on to occupy militarily the very regions the expelled people fled to, the West Bank and Gaza, from 1967 till today?
Whether you were aware of these points or not, they are historical facts. And they’re substantial reasons for seeing Zionism as a colonising movement, whose story is part of a bigger picture of western expansion into the global east and south, provoking resistance from local people.
Of course the Holocaust was one reason for European Jews moving in large numbers to what is now Israel. A few decades earlier, there were the pogroms in the Tsarist Russian Empire.
As you say: “Apparently it was these very same Jewish refugees who became the colonizers.”
Yes, that is part of what happened. But why the “apparently”?