“Subjective”
Our animal great ape cousins can reason but not as well as humans. So if an ape arrives at an incorrect conclusion on a task simple for humans does that mean the ape’s views “prove” subjectivity? Of course not. The reason for the discrepancy is their ability to reason is not a good as our own. What is a simple task for us can be very complex for them. We are better than orangutangs but this does not mean we don’t’ have our own problems as complexity increases.
Morals are one of the most complex phenomena humans have ever observed. They are codes of conduct necessary for civilization to be civilization. We can choose different morals but they are not equal in merit because the outcomes will be different depending on what we choose. If we choose codes of conduct where we end up nuking each other into oblivion…. immoral. Period. It’s not a subjective opinion. It’s objective. If we choose morals that enable us to expand to the stars, extend our lifespans, improve our quality of life, live happier, less suffering for sentient life, and so on…. moral. Period. Its not subjective. It’s objective.
The problem is it’s difficult to do the long term calculus of the outcome of some of our morals not that it’s all the same. Thinking that everything is subjective is cancerous to civilization as most outcomes are unfavorable. Only a small percentage of moral choices lead to a good long term result for human civilization.