While Parler and Gab were in use today by rioters, the usual suspects Facebook, Twitter, YouTube bear responsibility.

Article from LA Times:
What happened at the U.S. Capitol, with rioters disrupting the normally peaceful transfer of power between presidential administrations, can in many ways be traced back to the lack of urgency over such situations from social media companies.

For days leading up to the electoral college vote tally, Trump’s supporters had been talking about violence, several experts said on Wednesday. There were threats against elected officials and police officers, and talk of a second civil war from everyone from the "boogaloos" to self-styled militia groups.

https://apple.news/Ac4nA6bFuRRCLPW5IxWRzvw