Earlier quoted context omitted.
Yes, First Amendment protections apply to non-Americans. However, as you say, Assange is being prosecuted for conspiracy to hack computers, not for his speech.
The First Amendment probably does not apply to non-Americans with respect to their conduct abroad. https://en.wikipedia.org/wiki/United_States_v._Verdugo-Urqui... > The Court held that the Fourth Amendment's prohibition against unreasonable searches and seizures did not apply where United States agents searched and seized property located in a foreign country owned by a nonresident alien in the United States. Chief J…
So I'm not sure the same logic applies.