You simultaneously reject it and believe he wrote it to prove how unsustainable it is?

I reject the common interpretation of it, which is that “reverse fascism” is an acceptable response to “fascism”.

I give Popper the benefit of doubt by assuming that when he called it a paradox, he was presenting a proof-by-contradiction. In normal circumstances, a model arriving at paradoxical conclusions is proof of the model’s failure and a call for rejecting that model. If I assume Popper was not an idiot, I have to conclude that his paradox was not intended to support one form of intolerance over another, but was instead presented to demonstrate the subjective nature of fascism.

No ideas need to be shared where people don’t want to hear them. You are free to speak and I am free to not listen.

I think there is some confusion. Within the context of the paradox, those two sentences are mutually exclusive. The first one supports the paradox, while the second rejects it.

“No ideas need to be shared where people don’t want to listen” is a call for censorship; for silencing offensive voices. For creating a space where nothing offensive will be said, on the basis that “nobody” wants to hear it. In suggesting that offensive ideas should not be shared, you are supporting Popper’s paradox.

In the context of the paradox “You are free to speak…” Is a call for tolerating the intolerant. When you support my freedom to speak words you deem offensive, you are joining me in rejecting Popper’s paradox.