The reason behind the Hunger Games was that supposedly in the past, District 13 had revolted and was crushed by the government. The government then instituted the Games to remind each of the other districts of how much power the government had over them and how futile revolt was. So not for "no apparent reason", although the books did a much better job of clarifying this than the movie.
I took my 13yo daughter to see the movie after she had read all the books. Which were classified as Young Adult Fiction and are widely included on middle school reading lists. The primary themes of the story are about abuse of power, personal sacrifice, and the importance of hope.
I found the books to be quite disturbing, as I hate stories about situations where parents are unable to protect their children. However my daughter found the books very inspiring. She focused more on the fact that the heroine suceeded due to her intelligence, perseverance, and skills.
In this particular movie, the violence was not just gratuitous. It was a story device used to illustrate how abusive the government had become. A subtheme introduced the concept of how the government was able to victimize some by twisting them mentally to the point that they were willing to victimize others. This was not gore for the sake of gore and many of the deaths were not shown.
The movie has sparked a great deal of interesting dialog among the young people of our nation. Obviously, the question of whether such a scenario could ever happen here. If not that, then where are we headed? Is it okay to harm others for self defense or the defense of others. If American society was cast into the movie, would we be part of the problem, with all our excesses while much of the rest of the world starves and does without? How "real" is so-called reality tv, where days/weeks of activity are reduced to merely hours of viewing, and how does it reflect the director's/producer's philosophy more than that of the contestants? (Interviews with the author reveal that she came up with the story while flipping channels between the reality shows and footage of the war in the Middle East.)
It is not a fun movie, and while interesting and thought-provoking, is not what I would call entertaining. While the violence is a significant part of it, I did not go primarily to see that, and I find it rather insulting that some imply otherwise.