Combat experience is generally considered a good thing, at least in terms of being better able to succeed, and survive, in subsequent battles. But combat experience can be a bad thing in a long war. Historically, Americans become very agitated when a war goes on more than three years. This has been happening for centuries, and it happened after September 11, 2001. Popular support for the war effort sharply declined after three years. Even though the government said, from late September, 2001 on, that the war on terror would be a long one, this has not changed the impact of the Three Year Rule. If you can't get it over with within three years, you are going to face more and more voter and media opposition to the war effort. Go back and look at the history of all of America's long (over three years) wars and you will see this play out. It's happened in the war on terror, and the various theaters of conflict (notably Afghanistan and Iraq.)
The opposition is driven by frustration, paranoia (that some evil Americans are either purposely prolonging the fighting, or covering up their incompetence and inability to end the conflict) and mass media that sees all this angst as very profitable. Meanwhile, those who are fighting the war are seeing a different reality, or rather, THE reality. This time around, it's been more difficult to just go with the Three Year Rule flow, and it's altered reality, because there are all those blogs and other Internet based reporting by the troops. They are there, but what they see, hear and report is inconvenient. This is causing some dissonance.
The media response is that the troops get ignored, or criticized for being imperfect or unable to comprehend what they think they are experiencing. This is accompanied by a more critical attitude towards what the troops are doing. For those who haven't been there, it's easy to believe that combat can be a predictable place. It can be somewhere that has no torture, no dead civilians, no mistakes at all. But reality is messier, and this is the first war where inconvenient realities are colliding with media and political fantasies, for everyone to see. In the past, many people would back their fantasies for life. There are still dedicated Nazis and communists among us, along with those who accept many "scientific truths" that aren't. Thus the reality of what several hundred thousand American troops experienced in Iraq and Afghanistan doesn't always change the minds of people who have created a false image of what is going on. Kind of reminds you of religious wars, which we in the West believe we have moved beyond. We haven't. Faith can still triumph over fact.