The basis of a just law—what makes it just—is that it comports with the natural moral law.
The presence of a preamble is absolutely, totally irrelevant.
Sorry but the preamble is making an acknowledgement of preexisting natural moral law that it must follow.. it set the premise, the foundation, that naturally pre-exist its a statement of that fact ...it’s like the Declaration of Independence “we hold these truths to be self-evident”... its acknowledgement of preexisting natural law.. the law build by men must be built on foundation of natural bedrock ..else its arbitrary and has no true foundation..its nothing but whim of who has the power
look up the word preamble it has a function
the introductory part of a statute or deed, stating its purpose, aims, and justification.