In "War and Peace in Space - The Next 50 Years" Taylor Dinerman tells us hat the 'realists' of 50 years ago considered nuclear war all but inevitable. They were wrong. The 'realists' of today tell us space war is inevitable. They are also wrong. We will have war in space if the warriors of the world so decide and we fund their efforts.
The 'realists' tell us that we must defend our space assets. They avoid the undeniable fact that our current satellites are completely indefensible. They are fragile and their future location can be exactly predicted months in advance. Any organization with a launcher capable of reaching the necessary altitude and a sufficiently accurate control system can destroy any current satellite using a bag of marbles for the kill.
As long as a launch costs tens of thousands of dollars a kilogram, satellites cannot be hardened against simple kinetic kill systems. By adding propellent future satellites can maneuver -- if the timing of the attack is known. Even then, a slightly more sophisticated attack would probably succeed.
What the 'realists' that advocate space war really mean by 'defense' is to develop satellite kill capacity, which, of course, can easily be used for aggressive purposes. Any development of such systems by any power will inevitably lead to their further development by, at least, Russia, China, and the U.S., all of which have demonstrated satellite killers. The inevitable result of this arms race will be an completely vulnerable U.S. satellite fleet. Sound like a good idea to you?