An interesting thing, you've probably come across it in argument; when you argue "capitalism, J'accuse!" a rightwinger will retort something along the lines of "your moribund belief system has killed millions". Interesting: redbaiting as an argument is always burned on the outside, frozen on the inside, never properly cooked. Marxism is a moribund belief system, OK, but it's also vigourous enough to kill millions.
You can and should point out that stalinism in all its varieties is state capitalism. You offer that observation for a third party to contemplate. Rightist redbaiters can seldom cope with the concept, let alone accept it. The point of offering the Marxism Kills observation is to turn the tables. You have gone from attacking capitalism to defending socialism.
Think of things another way. If we are going to flatly condemn violence we must ask what political philosophy doesn't have blood on its hands? The current British government consists of Tories and Liberals. For centuries these two political traditions administered the British Empire, with all its wars, all its repression. They oversaw the slave trade, the Highland Clearances, the Potato Famine, the gassing of Kurds and the firebombing of Dresden to name a few incidents: and that only takes us up to 1944. Politics is the articulate expression of struggle, of violence. Every political philosophy is violent.
Even if we accept the dubious notion of continuity between Marx and Stalin (and the lesser Stalinist tyrants), the majority of humanity has been governed by bourgeois political philosophy for the last 400 years. The level violent death inflicted, from the grandest horror to the everyday holocaust of starvation, stretches far beyond Stalin's road of bones.
