No, it isn't. That those who join are majority of one party isn't because the military does any programming. It isn't fostered on them by the military, they foster the suggestion that no matter who is at the helm you follow them.
If Ds want the military to be mostly D they should join.
We can argue all day about the root causes of why the military is mostly made up of one party. There is not just one cause to begin with.
The fact is, it is dangerous, it is not democratic, and it's time to bring back the draft. That would end that right there, and also, when suzie and johnny middle class are going to be sent to Iraq, then, there is no Iraq. It's real simple.
Solves a whole host of problems.