Spiegel online has an article ("The Burial Brigade of Homs: An Executioner for Syria's Rebels Tells His Story")that gives a disturbing picture how deadly Syria's revolutionaries really are. It tells how this rebel group alone has executed nearly 150 government supporters in addition to 200 to 250 "traitors" from their own ranks. And this is only Homs and concerns only those who had first been captured and were then killed after a "trial".
Of course they mention government violence as an excuse. They also say that Syria has a very violent culture. But however you take it, it is clear that the rebels are contributing to the spiral of increasing violence too. And in a my bigger way than most of their Western supporters would like to admit.
Syria's government has its own claims on how deadly the opposition is. It talks about "6, 143 Syrian citizens killed by the terrorist groups and 1, 590 citizens who were kidnapped, the fate of two thirds of whom remain unknown".
20 June 2012: This article (In rebel-held Syria, revolutionary courts decide matters of life, death) reports about a more peaceful revolutionary court.