I'm pretty sure that Stalin has been post-categorized into the "Left-Wing" camp as he stood for "Socialism".
That one label is about the only thing about Stalin that could be classified as "Left-Wing". There has been an enormous amount of jostling amongst all "Left-Wing" political parties (globally) since then in order to differentiate themselves from Stalin.
"Socialism" is now very different from Stalin's view of it, just as "Liberalism" has now been watered down to mean anyone who isn't on the extreme right.
Arguing left vs right is not the way to view this problem. Seeing through the emotive labels and debates, and analyzing the actual behaviour will show you that personal power is the driving motivator, not any political ideology.
According to Plato "The measure of a man is what he does with power". Most of our world leaders at the moment aren't measuring up.