The London Review of Books has an excellent review essay on Trotsky, entitled Victory in Defeat:
An average British history graduate today will have been taught to evaluate revolutions on a simple humanitarian scale. Did they kill a lot of people? Then they were bad. Showing that some of those killed were even more bloodthirsty than their killers is no extenuation. Neither is the plea that violence and privation, the sacrifice of the present, may be the price of breaking through to a better future. George Kline dismissed this in The Trotsky Reappraisal (1992) as ‘the fallacy of historically deferred value . . . a moral monstrosity’. Monstrous or not, it’s a bargain with the future which, as anyone over 60 will remember, Europeans of all political outlooks were once accustomed to strike. But today ‘presentism’ rules, and the young read the ‘short 20th century’ as the final demonstration that evil means are never justified by high ends.
If pressed to take a side, I'd say evil means can sometimes be justified by high ends. But the question though is how far should we be willing to take the means of evil to get to a heavenly goal? How many corpses and atrocities before we say we have had enough and pack up our rifles? The Revolution will continue long after we have forgotten what it was all about in the first place.