In order for the US to remain a superpower the country needs to be able to project military strength to any corner of the world. During the cold-war this was essential to maintain the peace since the USSR was expanding and testing Americas ability to respond to flare-ups around the globe.
In theory I believe these bases are a good thing. During WWII America had a big problem being able to respond to the Japanese in the China Sea because of the lack of bases in the area. It was a long hard haul to establish island bases to operate from (see the battle of Midway, etc.)