This article argues against a particular form of compensation, not compensation in general. And in any case, "the free market" != "people are only motivated by

This article argues against a particular form of compensation, not compensation in general. And in any case, "the free market" != "people are only motivated by money". All "free market" means is that voluntary exchanges are not regulated or restricted by the government. Indeed it has nothing inherently to do with money, if you want to trade your labor for a pile of corn that would be a perfectly fine free market transaction.