One of my more interesting discoveries at Cato University was that many of the younger attendees rejected the existence of natural rights. This rejection is intellectually honest, particularly for atheists, but still abnormal for libertarians who generally consider such rights (life, liberty, and property, as first argued by John Locke) to be axiomatic. Some think that natural rights are ordained by God, and others think they flow from the "natural order", but few deny that they exist at all. Without natural rights, it's hard to argue that a government that respects life, liberty, and property is "better" than one that doesn't, because there's no way to define "better".
The rejection of natural rights by some of my fellows led me to consider the question further, and I've come up with a new (to me) approach to the issue from a very primitive "might makes right" perspective. Note that, as a Christian, I don't wholly subscribe to these notions, but they are consistent in result with my own beliefs and with the traditional "natural order" arguments I'm familiar with.
Essentially: natural rights are those liberties which are easier to protect than to take away. For example, it's difficult for government or individuals to control what I think, and it's easy for me to resist or ignore any laws restricting my thoughts; therefore, freedom of thought is a natural right. On the other hand, it's easy for an individual or government to thwart my alleged "right" to have someone else pay for my health care. Thus, the first is a natural right, and the second is not.
Now certainly sufficient force can be applied to create any "right" one may desire, but force is in limited supply and can't be used for everything. Witness the former USSR, and how difficult it was to use force to restrict private property rights. On the contrary, in America very little force is required to protect private property rights.
This argument doesn't claim that anything that can be accomplished by force is moral, but rather that anything that can be easily accomplished by force (or without any force at all) is acceptable. Deciding what is a natural right, using this structure, does not require a belief in God or in any particular "natural order", it only requires that it is possible to reach agreement on what things are easy and what things are hard to accomplish by force.