There is much that both libertarianism and its cousin capitalist anarchism have to offer in social theory. There is also much that is wrong, at least, in what libertarian/anarchist thinking currently is. The root flaw of any such system is that it views man as owning himself. In fact, God owns man, and man has a duty to God.
This is why even though there are many libertarians who are pro-life, they do not have a consistent philosophy behind their conviction.
From this fundamental error, other errors come. Libertarianism does not recognize cultural, national and religious values as property in need of preservation. The jurisprudence is seen as based on consent, the flimsiest of all possible foundations of justice; economy is likewise seen as expression of the workings of the market, which leads to the intrinsic value of products ignored and long term thinking impaired (cf. our mortgage mess).
The author is correct that liberarianism has been merely an opportunistic ally of the conservatives.
This is rooted in the agnostic/atheistic/secular humanist view fostered during the Enlightenment period that man's intellect is or can be the pinnacle of intelligence.
This is why even though there are many libertarians who are pro-life, they do not have a consistent philosophy behind their conviction.
While it is true that you will find a great many libertarians who are anti-abortion, the reality is that they are nearly always pro-euthanasia -- this IS NOT a pro-life position.