Well, it was your mistake #1.

Your mistake #2: the letter does not criticize Zionism (it is not even mentioned in the letter), but rather one specific political party.
And your mistake #3: you show Einstein as the only author of the letter, while there are about two dozens signatures in it. I doubt that Einstein initiated it or participated in its composition.
There is only 1 mistake on my part, that was to whom it was sent.
No, there are (at least) three mistakes on your part and I listed them.
In this letter, Einstein basically called Begin a fascist and accused him of creating a fascist state. He also inferred Zionists were acting like Nazis.
Nope, Einstein didn't mention "Zionists". Didn't I said it already? Yes, I said.
And I don't appreciate you trying to argue Einstein had nothing to do with this letter or its contents.
You can appreciate or depreciate your fantasies however you want. Good luck.
Your argument is bullshit. Your argument is just your opinion, not a fact.
And now you listed all your arguments.
Everyone who signed that letter, endorsed its contents.
Exactly - "everyone who signed that letter", not only Einstein. I hope that now it is clear even to you.