H_S:
You seem to agree that a person who fights for his country, for whatever reason, is automatically ensured a high moral ground for doing so.
Your thread title is about wearing the uniform. Wearing the uniform simply means you've taken the vow. A record of personal sacrifice living up to that vow is another matter enitrely.
I'll tell you what ensures a "high moral ground" IMO: Living by one's own priciples and respecting others who live by theirs.
If a person determines that, in the interests of the people of his city, he will put his own life on the line and become a firefighter, and he then does his job without making moral judgments, putting out fires and rescuing victims in houses, churches, porn shops, yes, I think that he has the moral high ground respecting his service to his city in his chosen profession, which may or may not have anything at all do to with the morality of his choices in any other aspect of life.
Now an observer may criticize and judge the firefighter for going on the call to the burning church, it being part of "satan's organization," or may criticize him for saving the proprietor of the porn shop. This observer may claim that the firefighter invited the judgment on himself when he made the decision to aid that immoral operation.
This same observer may also be unimpressed with the war record of a soldier who put his life on the line engaging in an "unjust" war.
Personally, regarding someone like McCain, while his war record should certainly not be the only or even the major factor in determining his fitness as national leader, I think it is clearly an objective factor in his favor that he has actually sacrificed for his principles and for his country to an extent inconceivable to most of us.