There was a ton of marxism/communism related violence in the US in the 20's, mostly centered around labor strikes. In general, that period saw much more violence and instability than the 70s. There was a literal battle win West Virginia between striking miners and the government:

https://en.wikipedia.org/wiki/Battle_of_Blair_Mountain

> Why must we wait for tragedy to strike in order to act?

Actions of the government (or other actors WRT policy changes) are given legitimacy by serving as a response to perceived existing problems. In essence, if there is no tragedy, there is no legitimacy to the action. Without legitimacy, the policy change carries less weight and is not effective. This is a basic reality of policy implementation.

The actions of banning white nationalist speech on tech platforms are given legitimacy by the recent NZ shooting, where (1) the shooter made numerous callouts to the white nationalist subcultures that these platforms foster (subscribe to pewdiepie, etc) (2) The content the shooter generated and streamed spread widely across nearly all distribution channels (FB, youtube, reddit, etc) despite censorship efforts, (3) We know that wide distribution of the extremist type of content that this guy distributed (whether its white nationalist, ISIS, or anything) in his actions inspires more people to extremism.