I have been pretty consistently pro-Palestine and critical of injustices perpetrated by Israel, but the anti-Zionist stance has always seemed to me to be counterproductive.

On the issue of just the legitimacy of the state of Israel, here's my basic stance: All land controlled by all governments was taken at some point through conquest (this is not a whataboutist stance, it's a tautology), but in the post-colonial era we all decided that might isn't right and that a mixture of international law, norms, and democratic principles should dictate the legitimacy of territorial claims. So, the Ottoman empire fell. The British seized control of the land of Palestine and retained a moderately weak mandate over the land (moderately weak in the sense that they were the essentially undisputed administrators of the land and had a military presence, but the territory would likely try to break away if the British tried to exercise significant control over it). With this moderately weak mandate, they pushed for the creation of the state of Israel that, by extension, I would consider a moderately-weakly legitimate state under the pre-WWII paradigm. Israel fights a defensive war against the Arab states and succeeds, converting the state of Israel as defined by the original 1948 partition plan from a weakly legitimate state into a properly legitimate state. At this point, the post-WWII frameworks kick in, and all the developments in the conflict past this point should be a function of that lens (ie. Palestine wrongfully denied sovereignty, illegality of settlements, etc.).

Zionism, in the most basic sense, is the belief in the creation of a Jewish state of Israel. There are more extreme and moderate versions of it, but that's all that it is at its core. Anti-Zionism is opposition to the creation of a Jewish state of Israel (I would not consider opposition to settlements or, strictly speaking, even to the accession of new territory into Israel proper past the 1948 borders after the two wars to be anti-Zionist itself). The anti-Zionist stance before the establishment of Israel was reasonable, but past that point is primarily a claim of one nation over the land of another nation. It's perfectly understandable at the end of the day for the Arabs and, particularly the Palestinians, to be upset about the whole situation and even to feel that a great injustice was done unto them. But that should all be relegated to the world of international affairs between established states. Ultimately, in my eyes anti-Zionism is not anti-semitic, but it's definitely anti-peace.