It also doesn’t really make sense to speak about non-existence either. One could describe a state of nothingness, but that is ultimately outside of our experience. There could be neither hypothesis nor thought experiment that would reveal to us what non-existence would consist of; as it would consist of precisely nothing.
So then, let me speak to the specificity of free speech, what it is, and why it needs to remain free, despite its consequences. Speech is not just our words, our language, but an ability to comprehend abstract ideas; ideas that don’t necessarily portend to the physical world; and are often metaphysical in nature.