I think it's a weird thing to refer to it as "right wing terrorism", when islamic terrorism also is right wing terrorism in a sense. Islam is based on much of the same conservative and fascist values as the far right, making them very much the same. An extremist muslim killing what they perceive as inferior people, is not much different than a western extremist right-winger killing what they perceive as inferior people.
Extremist left-wingers also think they have the right to murder what they perceive as inferior people, so this is all a problem with extremism which should be looked upon as a whole: extremists are dangerous, no matter their political background.