I'm pretty sure he's fully aware it's BS. He's also the guy who censored journlists and acrivits Twitter account on day 1 when he bought the company, and also the guy who canceled a command for a Tesla by a customer after a bad review.

Musk gives no shit to free speech, it's just a rhetorical argument, which isn't unheard of: https://i.redd.it/3b470c0htra61.jpg (note that I'm obviously not comparing Musk to Hitler here…)