That's really upsetting. Apparently the fight didn't look out of the ordinary. He took a few punches and then caught one on the chin, knocking him out. He was only 35 years old. It's really a shame.
Believe it or not, MMA
is generally much safer than, say, boxing, because fighters take less damage before a fight is ended. For instance, in boxing, it's standard for a fighter to be stood back up after being knocked down and expected to continue, whereas in MMA, once a fighter is knocked down, the fight is generally stopped immediately.
Furthermore, boxers tend to sustain much more severe head trauma because their pillowed gloves allow them to punch each other in the head repeatedly without causing any cuts -- guaranteeing that a fighter will take multiple head shots until they are knocked out, whereas in MMA, one or two punches to the chin/face can either KO a fighter or cause the fight to be ended on a TKO.
A lot of people think MMA is more brutal simply because they see blood. The reason you see blood is because the fighters don't where pillows on their hands.
Having said all that, any sport that centers around violent physical contact or pushing one's body to the limits is going to have casualties.