[Michael Chui]

Here's my take.

Begin with the assumption of an absolute truth. That truth and falsehood can exist outside of opinion. Therefore, there exists a real distinction between fact and fiction. Begin, also, with the assumption that human beings are on a search for this truth.

An opinion is an interpretation of reality; in other words, it is a potential fact in the viewpoint of some observant. If the interpretation is sufficiently in line with reality, then we would call it fact.

As observers ourselves, we are incapable of distinguishing fact from opinion (this is shown by either Einstein or Godel; take your pick); in other words, the accuracy of an interpretation with respect to reality is necessarily unknown.

Because it is impossible to be sure of the accuracy of any opinion, every opinion should be given equal consideration, because it is possible that it is closer to reality than one's own opinions.

However, a strong aggregate of opinion is considered trustworthy. Thus, because the majority of observers agree in their opinions, they thus consider those opinions to be factual. If you want to go deep, you'll note that this is, by itself, an opinion as well.

Thus, there are methods by which opinions may be considered more quickly and thus discarded faster. Some of such heuristics are the notions of authority, logic, and conviction. For instance, the opinion of an authority will outweigh the opinion of a stranger. A conclusion derived from a logical process outweighs a claim of self-evidence. And an opinion that agrees with one's own opinions is received with less resistance. These are shortcuts, but this doesn't mean they're wrong. On the contrary, they are frequently right, which is why they remain in use.

In short, the validity of an opinion is an opinion itself. Thus, the validity of a viewpoint is subject to the person ascribing a level of validity to it. Therefore, all opinions are as equal as you choose to believe they are.

Including mine.