I have a soft spot in my heart for pacifism. I think in general I would rather err on the side of pacifism than violence. But at the end of the day I'm not a pacifist. All I have to do is imagine some scenarios where I would be put to the test, and at the end of the day I don't see how pacifism is the right option, or the one I would choose.
That being said you want to make sure you don't cause more harm in the attempt to ward off an aggressor than would have been sustained through pacifism.
Also, strategy comes into play as well. I think as a strategy pacifism is great. Ghandi specifically spoke against pacifism as a strategy. I also have a soft spot for Ghandi, but ultimately his philosophy was anathema to human nature. And I think a philosophy that is incongruent with human nature is doomed to fail.
We call one of those philosophies Socialism.