Not really different from when the Air Force got spun off from the Army. There is already a space command division within USAF. As space continues to get more important for military/defense, it makes sense that you would want a dedicated service - it's different and important enough to warrant it.
I know there is the "non-militarisation of space" treaty, but let's face it, no one is really going to honor that (certainly not the Chinese or Russians), and in protection of your citizens you can't really do it.
I considered joining USAF instead of college, but went for my Aero E instead. If there was a Space Command.... might well have gone the other way.