打個比喻，如果同性性行為是犯法的，那所有的同性戀者都會有很高的重犯可能性，也就該被永遠的關起來。但這顯然是不道德的：法律不應逼迫一個人改變其性取向，正如其不應逼迫人改變政治立場。如果一開始的控罪就是不合理和不公義的，只聚焦「重犯可能性」自然也會得出不公義的結果。

In the course of the last few centuries, two main rival philosophical traditions have emerged about the nature of legality. The older one, dating back to late mediaeval Christian scholarship, is called the natural law tradition. Since the early 19th century, natural law theories have been fiercely challenged by the legal positivism tradition promulgated by such scholars as Jeremy Bentham and John Austin. The philosophical origins of legal positivism are much earlier, though, probably in the political philosophy of Thomas Hobbes. The main controversy between these two traditions concerns the conditions of legal validity. Basically, legal positivism asserts, and natural law denies, that the conditions of legal validity are purely a matter of social facts. In contrast to positivism, natural law claims that the conditions of legal validity are not exhausted by social facts; the moral content of the putative norms also bears on their legal validity. As the famous dictum, commonly attributed to Saint Augustine, has it: lex iniusta non est lex (unjust law is not law).