I've already touched on that issue, please read above.
I am instead however quite fascinated now with the question as to what is it in right wing extremism that motivates these men to go kill en mass. We always rightfully condemn there actions, but they too themselves are the victims, victims of being indoctrinated by this evil ideology.
Yes historically, both the Soviet Union and the People's Republic of China have the highest murder count, but it was the Nazi's who engaged in the most chilling and barbarous acts. I would rather spend my time in a Soviet gulag than be a slavic or Jewish person in a Nazi Concentration camp. In modern times, left wing extremists seem content on smashing universities windows to stop speech they find offensive, or assault someone wearing a Trump hat, but they do not go out and kill people in mass shootings like the far right.
What part of the primal unconscious brain is the xenophobia triggering that turns these men into mass killers? There is something about xenophobia, and the fear of being racially conquered that just motivates these men into pure murderous irrationality.