Because the context of "turning the other cheek" was not mentioned, because the actual story doesn't mean for you to not protect yourself or family.
But it was so obvious what context he was saying it in. And you're saying that as if its fact and widely accepted. The first Christians were pacifists so to be honest I trust their interpretation of Jesus, as they basically knew him. These other interpretations just spring out of the fact that pacifism is inconvenient, and people will find any way possible of justifying something they support.
EDIT: also the fact that he sought to see the best in people would probably mean he would despise the Bush doctrine.
To slap someone in return because they slapped you is one thing he clearly disagreed with, but to slap someone because you suspect they might slap you is another thing altogether.
I support(ed) the wars in Iraq and Afghanistan, but then I'm not a Christian.