Biiiiiiiig citation needed. By every available metric, right-wing terror attacks dominate the political violence numbers in the US. I don't know what fantasy world you've been living in, but frankly it sounds pretty sweet to me.
And mass violence is a worse problem than targeted violence. Whether or not you think they deserved it, the notable cases of left-wing violence in the last year have been individual targets. When the right commits violence, they roll up to a synagogue and gun down everyone inside. Or a gay nightclub. Or they slam a couple planes into buildings (yeah, if you're going to lump the left together, then you can't complain when the right gets lumped together).