I kind of agree with you and kind of disagree with you. You should be able to complain all you want. However, if explictly decide to give people certain rights when you complain about them using those rights it shouldn't hold much value. Which is what I think was the original point in the sentence you replied to.
But what's being alleged here is actual hostility and deception. If it's true, Zig being MIT licensed in no way removes their "moral high ground" (as GP put it) to make a post like this.
The fact that the Zig foundation wrote this letter condemning the actions of Zen's founder/employees - especially when they closed the letter with a call to action to return to Zig - shows that Zen's fork actually matters to them, that they don't believe it should remain functional.
Before this post I never knew Zen existed. Now I know it exists and am emotionally invested in it. And there's no such thing as bad publicity.