I don't know how I feel about this? If you willing to get in the cage, hopefully you've trained hard, and did so to test yourself and your skill set. Yes he was clearly getting beat up. There was a lot of fight left for the tide to change. There is a referee there for a reason. As a fighter your there to do what you trained to do. Your opponent can:
A. can quit anytime they want
or
B. Get his ass whooped and be proud enough not tap out, and take what he learned back to training if he decides MMA is something he wants to continue doing.
Either way I think the loser is getting robbed(in this case the winner), because now he had that experience and pride taken away from him because someone felt sorry for him and quit, when he clearly didn't want to.