The basic tenet of Chomsky's theory of second language acquisition is that humans are, so to speak, pre-wired genetically and psychologically with what he refers to as a "linguistic corpus", that is, a sub-organ that operates in the human brain which facilitates the process of understanding foreign languages.
Although generative language theories are widely accepted and tested both qualitatively and quantitatively, they base their tenets on Darwin's theory of evolution and infuse it in their own theory. In other words, generative language is a genetically given skill which develops as the individual evolves.
Counter-argument: Not all of Darwin's theory of evolution has been completely taxonomized to prove that it is entirely accurate. There are, in fact, quite a few missing links that render us unable to use this theory as a benchmark for argument in every aspect of Chomsky's theory.
Moreover, there is not enough biological nor neurological evidence to support the existence of a linguistic corpus, nor a "language acquisition device" within the human brain.
Finally, there must be some weight placed upon social learning. Those followers, such as Bandura and Piaget, contend that whether language is inherited by genetic acquisition, it cannot develop unless there are social inputs that facilitate its development.
Therefore, it all comes down to the life-long debate: Nature vs. Nurture.