Military personnel are trained professionals who put their lives on the line for the public good. In that sense they are like police officers or firefighters, in that they are (ideally) trying to do what's right, but do not get much of a say in where they are sent or what they are told to do. As a general rule, there is no reason to malign a soldier (or a police officer, or a firefighter) for carrying out the task they were assigned, not unless it's such an egregious task that no right-thinking, conscientious person would do it. Troops in the military should be supported because they (as individuals) fill a necessary and important role in our society.
On the other hand, the people who send troops into combat do not always do so for noble, high-minded, or civically responsible reasons. This is as true of police and firefighters as soldiers. Sometimes police are sent to break up protests or strikes to protect powerful interests, or used to oppress minority groups; sometimes firefighters are told to protect wealthy neighborhoods over poor ones; sometimes soldiers are sent into battle to advance the political and economic interests of powerful people, not because it's good for the nation as a whole. When wars are conducted for bad reasons, they should not find support in the populace as a whole, because it is a waste of public resources for personal gain, and an un-sanctionable risk to the lives of military personnel.
Sometimes, the only way to support troops is to oppose unreasoning war.
The reason a lot of (quote)liberals(unquote) use this apparently equivocating phrasing is that a lot of (quote)rightists(unquote) have adopted the strategy of trying to promote irrational war by leveraging support of the troops. In other words, they refuse to talk about the war itself — as though the war itself was unquestionable and beyond all criticism — and then try to induce shame and guilt by talking about our poor troops suffering in foreign lands. It's a bit like watching a parent beat a child, and then turn around and say: "Look how my child is suffering, please give me money!" If that parent really wanted that child to stop suffering, he would stop beating it; if (quote)rightists(unquote) really wanted to support their troops, they would stop sending them into harm's way for no good reason. But that's a complex argument that is difficult to make on the fly, particularly to someone who is being disingenuous in the first place, so most (quote)liberals(unquote) don't bother, and just try to push the question off.
N.B. In case you haven't noticed, I dislike McCarthyist, FOX Channel, 'dey be da bad people' labels. I'd ask you to leave them out of future posts.