Maybe the fight scene isn't so gratuitous/pointless/random afterall
My brother and I was watching this movie not too long ago and when we got to the fight scene at first we were laughing as it was going on, it's just so ridiculous how long it lasts. However, once it ended with Roddy Piper putting the glasses on Keith David, we thought that maybe that fight symbolizes how hard it is to get people to believe, or "see the truth" because they get so uncomfortable when you try to confront them with reality. Think about it, He nearly had to beat Keith David to death just to get the glasses on him.
I've talked to my friends and others about how there's a "ruling elite" that controls our elections, busy our politicians, and how cops are simply the "blue line" between us, the "Wage slaves" and the ruling class. That sort of talk makes folks uncomfortable, I see it in their eyes and body language. This is what that scene represents, the struggle to make people "see".
Only people with money say that money doesn't matter.