I don't think all, or even most, of our troops overseas are necessarily conservative. In my experience, most are apolitical, and those that are political are pretty evenly divided between Republicans and Democrats.
For example, I once listened to a political debate between three members of the 173rd Airborne. The two senior enlisted soldiers were both strong Democrats, while the lone officer was a Republican.
The "problem," if it is one, with soldiers is that they grow accustomed to the government taking care of them with health care, housing, legal assistance, food, etc. and often think that the government can do the same for the whole of the American people. Combine this with the strong authoritarian/hierarchal streak in most career military people, who are used to people simply obeying orders, and you have a potential recipe for a power-hungry, socialist politician.
Not to say all ex-military people will go this political route, but I certainly don't think recent vets are necessarily a solution to our country's woes.
And regardless of what we hear on right-wing propaganda outlets, most soldiers do not want to be in Iraq or Afghanistan to "finish the job" or whatever. Yes, it behooves career-minded officers and senior NCOs to say that, but the average Joe just wants to survive his tour and go home. For good.