Why is it that when someone praises a movie that makes soldiers look good, some people go out of their way to imply that the movie is "historical fiction" instead of possibly being an accurate portrayal of real events?

Have you read the book "Blackhawk Down" which has been described by the participants as factually accurate? Have you seen programs like the History Channel's broadcast "The True Story of Blackhawk Down" that goes into more historical detail than the movie could including many interviews of actual participants from both sides, including many Americans with straight teeth? Have you seen the movie? If not, then it strikes me that you're doing exactly the same thing that you blast others for doing, namely commenting on something based on what others say rather than doing some research to find out for yourself.

Most movies that portray historical events get a lot of the details wrong. "Pearl Harbor", in addition to wrapping a sappy love story around the attack, really botched a lot of details that it could've just as easily gotten right. Some of the worst include movies like "JFK" and "Nixon" that positively lie and distort historical events to foster an ideological belief.

On the other hand, some movies do go to a great deal of effort to portray historical events accurately. Before "Blackhawk Down", the most accurate movie that I can remember was "The Execution of Private Slovak" based on the book by Hugie about a little known incident in WWII. If you actually want to do some research on the topic, you can start here.