I dont see how they call it "mixed martial arts"
I can tell from experience that you're not right about this. It's quite different from a street fight and there's a lot of technique and condition required.
I sometimes train with a MMA fellow. Light weight dude @ around 160 pounds (same as me). If you use random thuggery against this guy, you'll be down in less than 10 seconds - he's an average fighter at the local scene but still he has about 10 different ways to counter any standard technique used in street fighting.
And believe me, this guy hits a lot harder than anyone I've fought on the street. A lot. It's not aggression gone wild berserk, it's the controlled delivery of pain. It's deliberate, thought out and downright devastating. I've had my arnold handed to me every time we've sparred.
Which is why Kimbo Slice goes down. He's a good street fighting brawler - goes up against a mediocre light weight MMA fighter. 14 seconds.
I can certainly see how someone uninitiated can fail to see the techniques used and the skills and physical conditioning required. However MMA is much, much more evolved than street fighting.