Not true, the first amendment is about more than political speech. See this article for a little of the history of free speech:

https://www.theatlantic.com/politics/archive/2017/12/two-con...

[Note in particular: After all, the genius of the First Amendment lies in bringing isegoria and parrhesia together, by securing the equal right and liberty of citizens not simply to “exercise their reason” but to speak their minds.]