Matthew and Luke also refer to Jesus admonishing his followers to arm themselves with swords: "But now if you have a purse, take it, and also a bag; and if you don't have a sword, sell your cloak and buy one." Luke22:35

And don't forget when Jesus cleansed the Temple by attacking and whipping people (John 2:14).

Jesus kicked ass, he isn't "history's greatest pacifist"  

"That would seem like a good idea if we weren’t talking about a sport where death is a real possibility. MMA fights bring the perennial possibility of serious brain injury or, in a worst-case scenario, death." 

I encourage you to learn about MMA before not only writing allegations like this but even before adopting these thoughts. MMA fights are not equivalent to toughman contests. The fighters are trained and possess a multitude of skills, including but certainly not limited to, strikes to the head. There are referrees and rules, and fighter safety is the top priority. It IS a combat sport, and there will often be blood, but there are fewer brain and eye injuries than in boxing BECAUSE there are a multitude of weapons a fighter can use against an opponent. That's what the "MIXED" in Mixed Martial Arts is intended to indicate. Every martial art from submission wrestling to Karate to Muay Thai to kempo to Brazilian Jiu-Jitsu, etc., converge in a well-rounded fighter, meaning there may be moments when they stand and try to make the other guy fall down solely with kicks to the leg, or a fighter may go for the knockout uppercut, but they can also use their ground skills to submit their opponents without any strikes whatsoever.

There have been over 1000 deaths in boxing and an unprecedented number of brain, ear and retina injuries.  In 70 years of MMA, there has been 1 reported death linked to the sport, and that's even accounting for the 55 years prior to safety precautions and real rules being implemented in 1993 in an attempt by the UFC to mainstream the sport. Even back when it really was "no holds barred" fighting, and a fighter could literally soccer-kick a doubled-over opponent if the mood struck - still, one death. Any untimely death is a tragedy, of course, whether it be one or one thousand, but I think you get my point, though. 

Further, if you have ever met a fighter, you would know these are skilled athletes. They're not thugs or gladiators or villians. Moreover, they are almost always Christians.

Having said that, I would also like to point out that the shirt is marketed to Brazilian Jiu-Jitsu specialists, not necessarily to "MMAers." As I would hope you are aware, in Brazilian Jiu-Jitsu, there are no strikes to the head or otherwise… just joint-locks, submission holds and chokes.  Sure, if a practitioner gets caught in a choke and the carotid artery is prohibited from transporting oxygen to the brain, he or she will pass out in a matter of seconds. As soon as the winner releases pressure,  the flow of oxygen is restored, and the loser wakes up. That's IF and ONLY IF the loser doesn't tap first. That's the purpose of a tap… to concede defeat and make the other guy let go.
 
If there is anything your article should have been chastising, it should have been the message the shirt was advertising… to not tap is to pass out, which has to be medical unsafe after a given number of times. (I have not researched this, but if you can assume things and write about them, so can I.) Oh but wait, if you chastise the shirt-makers for advising athletes not to give up, then you pretty much have to attack the Marines, too. "Death before dishonor," isn't that what they say? Maybe have a go at Nike, too, while you're at it. "Just do it"? Nah. It sounds like if it were up to you, it might be more like, "Just do it… unless you don't feel like it or if it could result in any sort of injury at any point in time."