But such support must come on a realistic basis. That is you have to support intervention of the sort a real imperialist nation will commit with all the side effects and consequences.
For example, I can imagine an intervention in Iraq that might be justiifed if committed by a United States in an alternative universe. But I have to oppose such intervention because I live in this universe, and have to consider the way the real U.S. generally behaves, and the consequences of that behavior. When I (retroactively) support the U.S. and allies in WWII, that means I am supporting them even considering the firebombing of Dresden, the bombing of Hiroshima and Nagasiaki, all the horrible things they did , but could have won without doing. Because I am juding of courese that a world ruled by the nazis, and facists would have been worse.
I think there is a hell of a burden of proof when naking this line of argument - one that can't be supported in Iraq or Afghanistan, or indeed in most of the U.S. interventions since WWII.