My local Republican congressional primary pits a libertarian against a nativist. Unable to stomach a nativist, I support the Libertarian candidate. Consequently, I have been reading Boaz's Libertarianism: a Primer to improve my understanding of libertarian philosophy. The book is extremely clear and light, suitable for bedtime reading. It also provides a useful foil for analyzing my own conservative views.
For simplicity, in the following I reduce the libertarian position to the level of Asimov's 3 laws of robotics. I recommend Boaz's book for a more faithful representation of libertarian philosophy. Asimov's 3 laws of libertarianism:
(i) People have the right to live their lives as they choose, as long as they do not interfere with the rights of others.
(ii) The government has the duty to protect its citizens' rights. In particular, it should protect them from attempts to harm their bodies or to harm or steal their property.
(iii) The government does not have the right to act in such a manner that it interferes with the citizens' rights expressed in (i) except in carrying out its duty specified in (ii).
Small government conservatives share the libertarian belief that minimal government is best. Like libertarians, they recognize that almost all government actions require coercion and thus some attendant loss of individual freedom. In addition, they recognize that government interference in the economy almost always reduces economic output. Where then do we diverge? Consider, for example, drug policy. A citizen's use of marijuana does not affect the rights of other citizens; hence, libertarians say that it should not be criminalized. I believe that decriminalization leads to much greater drug use and to use of drugs more dangerous than marijuana; I further believe that this greater drug use leads to large subsequent societal problems affecting many people including those too young to be given the responsibility to choose whether or not to destroy their own lives. I am therefore averse to decriminalization. Thus I differ from a libertarian in that I am willing to violate libertarian rule (iii) above if I consider the benefit to society is sufficient compensation for the coercive policy. A libertarian may now come along and convince me that my analysis of the costs and benefits of criminalization are incorrect (and I admit I have not delved deeply into this issue). A change of my position in favor of decriminalization, however, would not make me more libertarian. Because my decision is still based, in part, on a weighing of costs and benefits rather than a strict adherence to rule (iii), I am not a libertarian.
Constitutional conservatives believe that the government should enact no law which violates the Constitution, independent of any cost benefit analysis. In addition to respect for our founding documents and the rule of law, our reticence stems from our fear of weakening the constitutional safeguards of our liberties. Weaknesses that we create in our safeguards in order to pass legislation that we favor, can (and probably will) later be used to push legislation that we oppose. Most worrisome is the prospect that such weaknesses will eventually be exploited to erode our basic freedoms. All libertarians I have encountered are also constitutional conservatives. Where the Constitution differs from their libertarian philosophy, their recourse is typically to suggest constitutional amendment and not the (modern) liberal response of trampling the Constitution with activist judicial decisions or unconstitutional legislation.
The main battleground between conservatives and libertarians is on social issues (such as drug policy discussed above). For constitutional conservatives, this battle should take place only at the state level. Social issues are constitutionally the domain of state legislatures. As long as conservatives remember their constitutional principles, the libertarians are their natural allies at the federal level. Remembering this distinction between state and federal domains would lead to a greater conservative presence in the federal government.