You are confusing opinions with evidence and facts. Obviously you acquire knowledge by reading papers where people are doing research and experiments and presenting evidence, analytics and all the facts from which you can make your own conclusions.
OK, I don't think that this delineation is actually as black and white as you're making it out to be, given most subjects are complex enough to require nuanced interpretations of data/facts, but I'll give you that in some instances there is a fine line, and there are certain areas where there is a lot of disagreement even amongst experts.
Still, an expert, by definition is just someone that has "comprehensive and authoritative knowledge of a subject." You could argue that as soon as you've acquired enough knowledge on a subject to form an accurate opinion, you have yourself become an expert.
Although I'm guessing when you're referring to "experts" you mean "establishment experts." For example, your average doctor whose spent decades studying medicine as opposed to your online research on how to best treat/prevent a certain ailment (you didn't provide an example so I am just referring a fairly common one). What's the difference between your expertise and theirs? On one hand, they have decades worth of rigorous academic study and personal experience over you, on the other hand, you may have a "fresher" perspective that may be devoid of certain institutional biases. I would just strive to stay humble.
I may have looked more in depth into my condition (though that may imply listening to crackpots) than doctors who despite years of study may not be as in depth as me. There is a lot to the entire human body (which is why doctors refer people to specialists, but they need to choose the right specialist which isn't always easy)
