Libertarians hold that individual liberty should never be sacrificed in the pursuit of other values or causes. Compassion, justice, civic responsibility, honesty, decency, humility, respect, and even survival of the poor, weak, and vulnerable – all are to take a back seat.
Both rebuttals are worth a read. Here’s a sample from Boudreaux:
…libertarians argue that these other values and causes are best promoted by individual liberty, and that too many people who insist that achieving these other values requires the suppression of liberty are cynically seeking convenient cover for their own self-aggrandizement.
Horwitz makes the same point (though I can’t see that site now because of the Sopa protest).