Beauty may be subjective, but we're talking about facts: Is there a huge tower of naked girders in Paris? Does the Earth revolve around the Sun? Are there pink unicorns on Venus? Is there a powerful, invisible magician overseeing our affairs?
These are objective questions; empirical questions, unaffected by subjective feelings or personal opinions.
Again, saying "personal opinon" is just words. Next you will be defining "personal" as objectively visible processes in the brain, caused by genetics, and environmental factors, etc.
What is required to safeguard subjectivity is a logical construct. Basically the science of how a subjective statement is arrived at.
Subjective issues are about agency of decisions. So when the fact is that some things in the universe can turn out several different ways, regardless if it is a human being, or the weather, or anything, then it is a subjective issue what it is that makes the decision turn out the way it does. Meaning that the answer to the question of what it is can only be reached by choosing it.
Then you have defined a spiritual domain to which only subjectivity applies, as distinct from a material domain to which objectivity applies.