One of the trickiest concepts I try to get across in my English 102 sections is that the truth is not democratic – that is, just because something is popular doesn’t make it so. (Of course, lack of popularity doesn’t indicate truth either, though those Flat Earth theorists keep chugging along anyway.) A great number of people can be wrong just as easily as a small number. It’s counter-intuitive at times but absolutely vital to developing critical thinking skills, which are sorely lacking in public discourse at the moment.
A companion and even trickier concept is that opinions and judgments are not the same. (Short version: Opinions relate only to you and your experience, judgments are when you make statements based on certain criteria that draw broader conclusions.) Opinions really are all equally valid, because they’re only relevant to the person in question. Judgments must be based on criteria, which means it is in fact possible to prove them wrong, or at least challenge their validity. People mix them up all the time, and it’s a bit of a disaster, because while everyone may be entitled to their opinion, they are not in fact always entitled to make a judgment.
The trick is the phrasing – a lot of opinions are expressed as judgments. For example, if I say “That’s the best movie ever!” it’s likely it would be more accurate to phrase it as “That’s my favorite movie ever!” The best movie is a judgment – it would need to be based on some sort of criteria such as writing, cinematography, acting, you name it. Even if it’s not scientifically measurable – otherwise the Oscars would be determined in a lab – there are still concrete factors that can be weighed, and I can be called upon to either specify my criteria or give up and admit it’s really just an opinion.
I’m not saying that people need to vigorously police their language, just that if you find your judgment challenged and you can’t produce criteria to support it, or your criteria are found to be provably inferior, you should probably admit that it was really just an opinion and concede the point.