The left is only opposed to war and killing when it's honorable men killing evil leftists. Hitler, Stalin, and Mao -- all leftists who had no problem with killing when it was them doing the killing.
One of the evil left's favorite tactics is to confuse young people about the morality of killing evil leftists because they know it's the young people who fight the wars that defeat them.
It's the same principal as gun control. They're all for it because they know it's only honorable men whose guns will be controlled.