If he has a career ending injury, I think it was a brilliant move. I don't wish injuries on anyone, but anyone this stupid really shouldn't be playing the NFL.
Doesn't he realize that he is playing under what many consider a crappy contract, he is two seasons away from free agency, he knows one wrong hit could end his career, that if he has the surgery in the offseason he may not be able to play in his contract year, and if he doesn't have the surgery at all no one will touch him with a ten foot pole when he is a free agent? Ok, someone will give him a contract, but probably with little guarantees.
There is nothing brave about a player doing what is best for his body and risk career ending injuries unneccessarily when four of the best experts in the field told you not to play. Reggie Lewis did the same thing by listening to Dr. Mudge after his first cardiologist told him he had a life-threatening heart condition and it killed him. Merriman isn't risking his life like Lewis, but he is risking his career.