Are you an expert on a topic? What is it? How can you prove that you know enough on a topic to express your opinion. One professor of mine said, "I don't want to read about your opinion in your paper; I want to read what you found out." That's true unless you are getting your doctorate and know more than most people in the world. Is that extreme? I suppose, but not in the current environment where everyone expresses an opinion whether or not they know the subject.
If you really want to prove to yourself that you know a topic, then call an expert and see if you can follow the discussion. Can you even hold a discussion? As a corporate researcher, I used to look up experts in the federal and state government and ask them questions. I only did that after having thoroughly researcher it and talking to internal people to verify that I had good questions. Then I could usually follow the discussion.
What a joy it is to become expert on something over time. Think about it.