Briefly speaking, I’ll define a conservative as someone who wants to use state power to control the social and cultural dimensions of society, while allowing free rein to the economy, whereas a libertarian believes in complete abolition of state power, except for the punishment of force and fraud. The standard conservative objection to libertarianism is then that only certain social and cultural norms are conducive to a healthy society and that these norms cannot be left to the whims of civil society and voluntary association; they must be codified in law and rigidly enforced by government.
The main error in this way of thinking is the lack of faith it reveals in the power of one’s own culture. Let’s say there are objectively correct social norms. If some norms promote a healthier society than other norms, wouldn’t those norms prevail in free competition with other norms? If communities that follow conservative Christian teaching thrive, while others that follow socially liberal teaching fail, won’t the conservative communities grow and the liberal ones shrink?
One objection is that, in a quasi-Darwinian world of cultural competition, the culture that prevails may not be objectively the best, but merely the best at destroying competitors. For example, violent Islamists may just blow up peaceful Christians, even if Christianity is better. But libertarianism already addresses this in allowing for the right to defense of self and property. And if a culture doesn’t even allow self-defense, what exactly makes it so great? Or why should others shoulder the burden of defending it?