“Opinions are like assholes; everyone has one.” This implies all opinions are equally valid, because opinions are “just” opinions. Often the speaker goes on to confuse or conflate facts with opinions: for example, “it’s just your opinion that human beings didn’t walk with the dinosaurs.” No, it’s not an opinion; it’s a fact.
Opinions are conclusions drawn from available facts. Difference in opinions arise because people have different degrees of comfort with subject matter, incomplete access to facts, or incomplete understanding of the facts they know. There is no such state as perfect knowledge, so every opinion is flawed to some extent. Reasonable people can disagree about opinions, therefore we accept that opinions are subjective.
While opinions aren’t facts, their merit can be weighed. If an opinion is based on outdated or incorrect information, or if it contains logical fallacies, it should be discarded by the holder of the opinion and discounted suspect by the audience. Opinions based on many well-understood facts merits more attention than opinions based on few facts. Opinions that ignore facts that undercut the opinion should be ignored.
Facts are facts regardless of season, time of day, or political party. Some facts are firmer than others. Gravity is a fact; a liberal will fall to their death if dropped from the Tower of Pisa as surely as a conservative will. A fact is a fact whether you believe in it or not. Just ask Wile E. Coyote.
Opinions are conclusions drawn from available facts. Reasonable people can disagree about conclusions, and so have different opinions, but two reasonable people cannot disagree about facts.
Assholes are facts, and everyone needs one. That assholes are ugly or funny or weird is an opinion. Only an asshole stubbornly clings to a bad opinion like the US is a post-racial society.