When weighing people's opinions, expertise should be rewarded but commitment should be penalized.
Committed people have a psychological need to prove themselves right and to discount contrary evidence. This is due to a combination of conscious and subconscious factors: enhancing one's social and career standing, making oneself feel better about the invested effort, etc. Among people who spent a decade or two arguing in favor of a certain theory, not many would be comfortable admitting they were wrong all along.
There is a period of time when someone is already an expert but not yet committed to any particular belief. This is an excellent time to listen to their opinions. Unfortunately, this period is usually quite short for most people.
Sometimes (as in this case), the commitment is quite obvious; at other times, it may be hard to detect it.