Natural Law does contain serious weaknesses, first of all it may be regarded as idealistic; Aquinas says that humans have a “tendency to do good and avoid evil”, however provides no basis for this assumption and no evidence to back it up. Furthermore it is based upon single idea of human nature. To be pragmatic however, people have different lifestyles and opinions. Aquinas seems to presume that we are inherently all the same and fit under the bracket of one human nature. For example homosexuality would be persecuted under Natural Law because it doesn’t seek to reproduce, but most would now agree that there is nothing morally wrong with homosexuality.
In being an absolutist theory, Natural Law is ignorant of the situation and thus may fall prey to many of the moral “pitfalls” that come with being unable to employ moral flexibility based upon the situation. Proponents of the theory might say that Natural Law tells us, as humans, to push and become the best we can be. We are told to aim for a purpose and maintain an ordered society. This is important for maintaining an ordered and moral society. However Natural Law could result in poor outcomes if the primary precepts are rigidly adhered to. In terms of sexual ethics, Natural Law would rule out contraception, as an example: the removal of contraception in many strictly religious countries has already led to more and more cases of AIDS across the globe.