“Because of the diverse conditions of humans, it happens that some acts are virtuous to some people, as appropriate and suitable to them, while the same acts are immoral for others, as inappropriate to them.”

Yeah, so!?! What does history tell of such acts and conditions along with the related consequences? How does natural law relate here? Are the rights of the individual, in fact, violated?

Sadly, the religious "right" are oh so wrong on this point.

The 'moral' argument is a subjective argument as 'virtues' vary from culture to culture. This is something most fundamentalists need to come to terms with. Interestingly enough, persecution of the supposedly 'immoral' is not considered immoral... (?)

The idea that virtue is subjective is something of a misstatement, based, in part, on the common concept that virtue is interchangeable with values. The initial substitution can be traced, I believe, to Nietzsche and then Max Weber. In that construct, then, with the death of truth (an absolute condition and a virtue) we have the absence of good and evil and virtue and vice. With the acceptance in modern society of the substitution, Western society also accepted the concept that all moral ideas are subjective and relative, which is quite at odds even as late as the Victorian period in England. For the Victorians, virtues were fixed and absolute; this is at odds with Aquinas but not all of Western thought. Virtues included such things as work, discipline, thrift, self-help, and self-discipline. Virtue was the force behind manners, and manners the force behind a civilized people. Contrast, if you will, today's cultural and social exchanges with that of the Victorian period, particularly in the arena of criminal behavior. With the imposition of Victorian virtue, crime fell dramatically as all classes embraced the virtue of honesty and integrity. We would do better to consider that same condition.