Disagreement about natural law doesn’t make it subjective, it just shows we’re fallible humans trying to understand objective truths.
But here’s the thing: if natural law is merely personal preference, then your view carries no more weight than mine, or even someone who wants to harm you. The Constitution was built on the idea that some principles of justice actually exist and are worth defending together, not just accommodating everyone’s opinions.
We can reason toward these truths even when we disagree about the details.