A couple of months ago, I read an article online. Recently, I thought back to it. It differentiated between two different types of opinions. The first regarded things like ice cream flavours. The article suggested that opinions on flavours of ice cream cannot be wrong. That is false.
At a glance, it seems as though an opinion on what flavour of ice cream tastes best is something someone is entitled to - it is pointless to debate and there is no wrong answer. However, your opinion on what flavour is best simply has to do with how it affects your brain. The best flavour ought to be the one which yields the most positive response. This will vary from person to person, but with numbers, a trend would show. I cannot conduct an experiment on this, but I can outline what one would need to do.
First, it would have to identify the most common ice cream flavours. It doesn't matter if Double Chocolate Raspberry Coconut Nuclear Waste Jam is an amazing flavour - it's just not well known. For the purposes of this outline, I will stick to vanilla, chocolate and strawberry.
Second, the flavours would need to be balanced. Vanilla ice cream tends to be somewhat plain, so its flavour, in an experiment, would have to be increased - more vanilla extract, perhaps. Once all of the flavours were approximately the same strength, testing could begin.
There are two ways that this could be tested. Subjects could simply try all three and state which one they prefer, but that is open to bias or stubbornness on the part of the test subject. A more accurate way to do it might be to measure the subjects' brain activity. I'm not a neuroscientist, so I can't go into much more detail than that.
Finally, the data would need to be analyzed. If one flavour stood out from the others in terms of best reaction, and the testing group was large and diverse enough, then it could be safely said that that flavour was better. If one flavour actually achieved a majority of people reacting to it best, and the test could be replicated over and over again, it could be safely said that that flavour was the very best flavour of ice cream.
Opinions on which flavour of ice cream is best are no more exempt from the realm of fact than opinions on things which are already known, such as the existence of a god, global warming or astrology. It is simply that getting facts on ice cream is much more difficult than getting facts on whether or not the apparent positions of planets along the ecliptic affects your personality in a significant manner.