Philosophy at its Worst
Natural Law is defined in different ways by different people. The gist of it is that you can observe things and, from this, determine how God wishes us to use these things; that in creating things, God provided clues about their proper use.
This applies for humans as well; that we can observe facts about ourselves and, from this, know with certainty which behaviors are morally right and which wrong.
It goes without saying that each person will come to a different conclusion, and this is exactly what we find. Therefore, I reject Natural Law; it is utterly useless for showing what is true and for revealing God's absolute moral law.
While we can observe what works and what doesn't work, we should not assume that God's will is always in harmony when things work out. Thus, while repressive tyrannies are effective in controlling a populace, this does not mean God looks favorably upon this.
The only trustworthy source of moral, spiritual, and religious truth is divine revelation, revelation from God about his desire, plan, and purpose. And the only trustworthy source of divine revelation is the Church,the Christian Church,having infallible teachingpassed-downfrom the apostles.
Elsewhere, I provide detailed discussion of Catholic use (misuse) of Natural Law with quotes from Catholic documents. St. Thomas Aquinas based his massive Summa Theologicaon the philosophy of Aristotleand on Natural Law. The Catholic Church uses Aquinas and Natural Law as a basis for some key doctrines.