Well the site is reason.com....so one would naturally assume a propaganda piece supporting the right-wing agenda...but the information contained actually did quite the opposite.
It was almost a compilation of entirely right-wing wrongs....the last paragraph tried to blur the lines but anyone with an iota of critical thinking skills can clearly see the righties are nuts.
As for your interest in the right being more violent than the left....just re-read the entire story.
Of course you may arrive at the same conclusions...some people are incapable of thinking beyond what they've been indoctrinated to think.
Or it could be as innocuous as a Rorschach test....perceptions differ.
Your inclusion of communists and socialists are irrelevant to the discussion but you're certainly free to prove otherwise. The onus is on you.
You could have saved a lot of typing and said "no, I cannot support my position with a study"
You appear to be making the claim so it is on you to prove it.
I will support my position about the Russian Communist Party. Lets start with Stalin political victims:
Stephen G. Wheatcroft, "Victims of Stalinism and the Soviet Secret Police: The Comparability and Reliability of the Archival Data. Not the Last Word", Source: Europe-Asia Studies, Vol. 51, No. 2 (Mar. 1999)
death penalties, 799,473;
camps and prisons, 2,634397;
34,228 death penalties,
2,066,637 sentences for 0–1 year
4,362,973 for 2–5 years
1,611,293 for 6–10 years
286,795 for more than 10 years
I think the National Socialist German Workers' Party (NAZI) work is well known, but I can support with references if needed.