I think if anything, MMA fighting would be far more barbaric than boxing but in the end, it all comes down to what you prefer. Take one or the other, each of those two sports have their beauty and skill involved..
MMA definitely looks more barbaric, at least in the striking dept., but it is often argued that boxing is worse. The argument seems logical to me, though a neurologist would probably be the only one qualified to address this. Boxers take repeated head trauma, sometimes suffering several flash KO's in a single fight. Usually, in MMA, if a guy gets dropped solidly, the conclusion of the fight is imminent, such as what happened with GSP and Serra, GSP vs. Hughes, etc. In boxing, the guy gets his count to recover, just to get hit in the head again. MMAists don't take that many shots to the head, but it is easier to get KO'd. So the question for the neurologist is, which one does more damage, sustained head trauma over a greater period of time, with recovery, or getting rocked, pounced, and stopped.
Beyond the striking arugment, there is also the perhaps more relevant fact that some MMA fights are virtually strike free. Look at Randleman and Shogun. They have both proved that they can put guys to sleep on the feet, but when they fought, there was not a single punch thrown. In MMA, some guys end up appearing to be on the brink of death, but a lot of guys come out of it unscathed, win or lose.
I tend to think boxing is worse for your long-term health.