Perhaps not Twitter's fault per se, but I don't mind seeing it die a lonely death for the only reason that it gave voice to the truly despicably racist, homophobic and planet hating assholes all around the world.
I have the exact opposite problem with Twitter. They need to get out of the business of trying to police speech. As you point out they completely failed to do it effectively but I think it is an impossible task for a global communications network in a still highly heterogeneous world.
Yep, gave a voice to them and only them.
Not to mention all the worst speech-policing neo-Puritans that San Francisco has to offer.
And next, we could get rid of the internet, telephones, and mail. Then, finally, the people we don't like will have been silenced.