I assume you are referring to Iran? It doesn't take 100,000 U.S. troops to serve as a buffer against Iran. One aircraft carrier is enough to give Iran pause. The battle of ideals will be decided by the success or failure of Iraqi democracy.
You mean by Iraqi subservience not Iraqi democracy. Look at the hundreds of thousands of people who took to the streets of Iraq today, even with a 150,000 occupiers in the country, has the overwhelming will for their expulsion been heeded by the suppsoedly sovereign and democratic government?
A military presence does serve as a very real and tangible buffer against Iran from the american perspective, this is something we don't even need to discuss, the people in the Pentagon responsible for the handling of miltary operations themsevles have upheld this theory consistently. It cannot be dispelled by a few quixotic citizens who still believe that there is even a residual degree of benevolence in the upper echelons of american power.