MM's linked post is bang on. Independent air forces were needed first of all because the other services could not agree as to whether an aeroplane was a large horse or a small ship, and it never occured to them that it was neither.
There is also a completely delusional argument that, by getting rid of an independent service, the costs associated with developing air and space systems and training their operators will disappear. They will (at best) be transferred to other services. So who now sponsors research into radar or AAMs or military aircraft engines? The Navy? The Army? The DoD/MoD? Who advocates for it?
Another completely empty argument is that air missions "support" the Navy or the Army. First, there are air missions that are air missions, like air defense, long-range strike and strategic ISR that support the entire war, not any specific service. Second, the argument can be turned on its head in the case of a carrier Navy - a Navy battle group is essentually devoted to the protection of an air base. But above all, air, sea, land and space operations are interdependent - at times one or the other leads, that's all.
The most important argument for maintaining separate services is the need for a culture that fosters the development of people. As has been pointed out, a huge flaw in the US Army's desire to acquire a large UAV force is that their operators will be neither aircrew nor ground-pounders, but Intel pukes, REMFs in a dead-end job, since the Army clearly believes that a trained ape can fly a 1.5 ton armed UAV in a dense battle environment. Are you going to see operational skills develop? New and better CONOPS being devised?
This might also be interesting...
http://www.aviationweek.com/aw/blogs...entId=blogDest