Agreed a bit, not fully, but if someone is against it, then there is already a bias. For someone who is not involved and not against it, just want to compare them, I argue that person might not know and understand it completely. So a bias is natural. So taking that as an argument to discount the credibility, I am not entirely on board. However if someone is so much biased, that it looses all judgement of positive and negatives, and only provides one side of the story, then I am 100% on your side of opinion.