I'm personally a big fan of UFC. I love seeing the most skilled fighters (who are also athletes, by the way), push themselves to their limits.
It's important to realize that the UFC is mostly a combination of sports that are already present in the olympics: boxing, wrestling, judo and tae kwon do. I have never heard an uproar about these sports being in the olympics. UFC also permits ju-jitsu, which is not in the olympics.
People do get injured fighting in the UFC, but many people claim that it is in fact safer than professional boxing. In boxing, you can be knocked out but then recover and continue to take blows to the head. The additional head injuries after already losing consciousness can result in profound and permanent damage. This is not a risk in the UFC because because once a person becomes unable to defend themselves, the fight is over. The same can be said about a comparison between UFC and football, by the way.
All this being said, I do think that some fights should be stopped before they are. I have seen some gruesome injuries that should have resulted in a stoppage but didn't, and that upset me. When this occurs I feel that the UFC is not acting in the best interest of the athletes, and is reducing itself to selling a spectacle instead of a sporting event.