I don't understand the phrasing of the question.
What is what on his own?
First, calling the moral writings of people like Orwell, for instance, mere opinion is to greatly understate what it is he (and others) wrote. Secondly, the flaw in your logic is that if there is such a thing as objective morality and ethics, and this truth can be recognized and understood by man, then there is no reason why man himself cannot intuit it on his own.
Hence - What is that "on his own"?
How can a person intuit something "on his own"?
Some might, but I don't think most people give it much thought. In fact, I think most people go on knowing that what's right for them isn't always right for others, and get along just fine with that. Hence, being content with the subjective nature of their righteousness. In other words, Absolute Truth doesn't factor in for most people. For them, it's about what they believe is right at the time.
When directly confronted with a question like "Do you believe that you know The Absolute Truth?", few people would reply affirmatively, as this does seem a preposterous question, answering it affirmatively would be nothing less than the declaration of omniscience.
Nevertheless, for all practical intents and purposes, people do believe that their opinions aren't merely opinions, but The Absolute Truth itself; ie. that the way they see things really is "how things really are", and not just a reflection of their subjective preferences.