There is a saying, "Opinions are like assholes. Everyone has one." It is about as true a saying as I've every heard.
But that is just my opinion...or my asshole. Imagine if everyone spouting opinions as if they are truth had to end their statement with, "But that's just my asshole." Perhaps they'd think a bit more before speaking.
Spouting crap with conviction is particularly a folly of youth. Even my two-year old son will tell me a blue crayon is red and defend his observation adamantly until he is distracted by a Cheerio or fruit snack.
I write all of this with conviction knowing that I am about opinionated about things a person comes. But I have grown to recognize my opinions as only my opinions. I have also grown to recognize that no one really likes to hear other people's opinions unless they mesh with their own. So you are better off just sitting in a chair muttering to yourself than piping up with your opinion about anything. Then people will think you are a pretty astute and amiable person.
That being said, I imagine it would be a pretty boring world if everyone had the same opinion about everything. There would only be one religion (if there were a religion at all), one political party (if there were a government at all) and one gender (if people existed at all). You wouldn't have marketing or advertising, because there wouldn't be anything to convince people of. And most importantly, there wouldn't be any assholes.
That is hard to imagine.