Why in the US is the military the only (or at least main) instance where it is not only acceptable but highly encouraged to say, "I dislike X but I support the people who perpetuate it"?

I dont know that such a notion is only found in terms of supporting the troops. A similar sentiment often expressed in the US has to do with unpopular speech and First Amendment rights - the "I hate what neo Nazis or the Westboro Baptist Church or whomever has to say, but I will defend their right to say it."

I believe that this may stem from a misinterpretation of the problem. I dislike war but I support our troops. I don't like war, but it is naive to say that war will never happen. So despite my dislike of war (I doubt anyone likes war), I have come to accept that a military is wholly necessary in order to maintain our freedoms and liberties, and respect people who are willing to risk so much in the name of those values. Another example: I don't like taxes, but I know that they are necessary to pay for the services and military the government provides, so I support taxes.

This is coming from Evelyn Beatrice Hall who wrote a biography of the French philosopher Voltaire, The Friends of Voltaire, in 1906. She coined this famous saying: I disapprove of what you say, but I will defend to the death your right to say it.

Your question is rather vague but I believe what you are asking is:   "Why do Americans say they dislike war, but think highly of their soldiers?"   As an American who respects soldiers, my answer is "War sucks, but these are our guys."   EDIT reflecting added question details:     There are several reasons for why soldiers are treated differently from the other examples.   1) Patriotism: The military is pretty much universally viewed as, perhaps, the most patriotic organization in the country. Most who join are considered to have done so out of patriotism and anyone who derides them is considered to be the opposite of patriotic. One can get away with criticizing the war and the reasons for it, but criticizing the soldiers themselves is about as politically incorrect as rape jokes.   2) Politics: In addition to looking like an asshole on the political correctness scale, there is an added reason why no politician (or celebrity for that matter) can ever afford to take an "anti-soldier" stance. If you count up all the people in the military, their family, their friends, it adds up to tens of millions of voters (where as the IRS only has less than 100,000 employees).   3) Compensation: Unlike the Monsanto bioengineers or Wall Street investors, soldiers are not out to get it rich. In fact, when one considers the rigors of training, relocation, job difficulty and potential risk of death, they are hardly paid at all. Therefore one cannot accuse them of being greedy bastards selling out their morals. Black Water mercenaries (or whatever they call themselves now), earn far more money than the average soldier, and are also not viewed nearly so highly (overall quite negative, most likely).   4) Culture: Our culture (movies, television, novels, etc) have all raised us to respect and admire soldiers. The politicians might be (and often are) portrayed as scumbags, and perhaps the higher level officers as well. But even in the most anti-war themed movies, the regular soldiers themselves are almost always protagonists.