The meaning of 'opinion'

Why do people not understand the significance of an opinion?

Simply put, there is none.

"A view or judgment formed about something," says the Apple dashboard dictionary; I'm not going any further than hitting F12 to substantiate my claim here. It continues: "Not necessarily based on fact or knowledge." That says it all! An opinion is just something that someone thinks. Can any assertion be more vague? Maybe the opinion is based on some concrete evidence, or maybe it's based on person experience, or maybe it's based on total BS. The point is, in all the above scenarios, equally valid opinions can be formed. I say they're equally valid because the only criteria for an opinion to be an opinion is that someone, anyone, has to think it. That's about the lowest requirement of support I can possibly imagine.

Why does it matter?

It annoys me to no end when the crux of an antagonist's argument is, essentially, "You shouldn't have that opinion because it differs from my opinion." No. Wrong. Dead wrong. I can have an opinion that differs from yours, and honestly, if your only retort to my standpoint is that my viewpoint conflicts with yours, you don't actually have anything useful to say.

Everyone is completely entitled to have an opinion about whatever cock and bull issue they want. If it's your opinion that the sky is ruby red, Santa Claus exists and the earth is 6000 years, fine. Fantastic. I'm very happy for you. If you want to convince anyone else of your opinion, you'd better have something more to say than "I think blah blah blah."

Otherwise, shut the fuck up.