This sounds like the usual, Self Defense angle of romanticizing the usual, death match scenarios that hardly ever happens. Street fights usually ends when someone is KO'ed and are usually a lot easier than fighting an equally skilled competitor in MMA or other full contact sports fighting.
MMA fighting is indeed, trying to beat someone to death. Do you think that an MMA fighter is not putting all of whatever power he's got in trying to throw his fist, elbows, knees, etc. into his opponent's face, head, body, etc.? Or do you think that he's only putting in 50% or even 80% and then saving that 100% power & intensity only for the streets? Especially when tens of millions of dollars can be riding on their fight. Hell, even amateurs fighting for no money are fighting with everything they've got. The only reason no one dies is because the fight gets stopped and it's over.
If you had to defend yourself in the street, where you had to fight...what's the goal usually? Incapacitation probably, which is basically a KO. How is an MMA fight, where fighters strive for this incapacitation, any different than in the street? Once you KO your attacker in the street, are you going to keep soccer kicking his unconscious head until he goes into a coma or dies? Same with inside an MMA cage, the Ref or even the corner, stops the fight. In the street, many times, other people, bystanders, police, etc... stops the fight or even the winner, stops attacking someone who's KO'ed, on his own. I have around 700 videos of real fights and adding more almost every day. Only about 2-3 where someone actually died from being continuously beaten to death, and there overseas mostly, in really poor countries. Another 2-3 are from someone getting KO'ed with 1-2 punches and they crack their head on the cement and dies later at the hospital; these were unintentional deaths.
This covers the "beat the living crap out of you", the "kill you" and the "maim you" and "rape you" parts. Mugging and robbing, well that's easily resolved by just handing over your valuables, most of the time. If they didn't just suckerpunch you or surprised bashed you on the head with a brick to take your money, then they're probably not looking for a fight to begin with.