Suppose the question is which singer is better, Elvis Presley or Frank Sinatra. There are many ways to try to answer this question. One is to ask people which singer they think is best. But this poll would not be definitive. Even if you found out that most people preferred Sinatra, you could still argue on other criteria that Presley was the best.
But suppose "best" is now defined as the singer most people prefer. Now the poll is essentially the only good way to answer the question; other ways have value only to the extent that they predict the results of the poll. Once the poll is performed, it is irrelevant to aruge that Presley had the better voice and better singing tecnique.
NEXT: Invalid Arguments