If you are a non-fictional narrative writer, there will always be books written on the same subject matter as yours. You need to establish your brand, your style. Many Writers compose their works based on different perceptions. Some may just be personal opinion, others based solely on facts or spiritual beliefs, etc. For me, the topics I write about are based upon a combination of "confirmed" data, facts, and experience tied together with real-life stories and situations, along with education. That's my brand, my style. The brand I want my readers to know about. With that said, no writer's opinions are wrong. An opinion is a view or judgment formed about something, not necessarily based on fact or knowledge. When it comes to opinions, there is no right or wrong, because it is the opinion of that individual, and many discussions come about due to difference of opinion. However, it's never about right or wrong because everyone is entitled to their opinion. That's exactly what book and movie critics do. State their opinion. Remember, you can please some of the people some of the times, but never all the people all the time. Stick to your style, and in time, you will develop a following of those who like your brand, your style. As you write, understand your readers will be reading other works by other writers, it is important that they know your brand. That's who you are, what you are trying to sell. Your goal is to make your brand well known, and stick to it. Enjoy the experience of writing.