Yeah, a state that is constantly in war(s), paints the target countries du jour as the enemy building racism against their citizens, tolerates torture and police shootings (letting officers that do that shit free), and is obsessed with violence and gun ownership, suddenly is worried about "spreading extremism".

What about Stalin?

What about non-white supremacist manifestos? They do exist, you know.

How much history would you erase due to your belief that words are capable of 'infecting' (presumably) lesser minds?

There's no evidence that manifestos spread "extremism and terrorism like a virus". Words are not able to infect people against their will. There are only ideas, and they can only be fought with reflection, more words and more ideas.

In the end, white supremacists and other kinds of supremacists existed before the internet. By supporting China-style censorship you're not actually eliminating those ideas, or even stopping their spread.

Sounds like a genius plan.

Don't ban easy access to guns, don't change a crazy individualistic/every man for themselves/violence loving culture.

Just hide the manifestos, that should work.

(Cue the "one doesn't prevent us doing the other" answers).