Somewhere along the line, the party appears to have lost its ability to tap into the fears and aspirations of a part of the electorate, what we may have traditionally thought of as the working class vote... Whether it is policies, communications or candidate selection, Thornberry's tweet has only highlighted a problem that has been growing for a while.
Perhaps Twitter should consider looking at verified accounts in a completely different way... maybe it should be a compulsory part of signing up for an account. If you've handed over government issued identification papers during sign-up (driving license, passport etc) to prove who you are, you're significantly less likely to start sending out death threats - unless you're stupid.
Facebook and twitter came at a pivotal time in history. The chicken or the egg theory can be applied here in asking: Did twitter and facebook help revolutions grow, or did they help track people involved in uprisings? (In both the case of the Arab uprisings and the Occupy movement.) I would say both.