While your assertion, "Theology isn't personal opinion" is correct, the verse you quoted has nothing to do with that assertion.Theology isn't personal opinion. “Knowing this first, that no prophecy of the scripture is of any private interpretation.” 2 Peter 1:20 (KJV 1900)
Peter was talking about prophecy specifically. Biblical prophecy does not have its origin in human interpretations. Many people misinterpret that verse.