Human Nature
Most people miss the point entirely, human nature dictates that we each protect that which we see witihin our own sphere of influence and go after the things which will benefit our cause the most.
Genereally speaking cooperation between two groups can only be acheived and maintained by a higher authority, in this case the government.
The problem we have is that the higher authority must be flexible enough to make quick decisions in time of war but far sighted enough to maintain the armed forces in a state which is suitable to the kind of unconventional warfare we are seeing in both Iraq and Afghanistan.
Long story short, stop bickering over which force is the best and start battering our governments to manage the forces better and supply them with what they need to get the job done.