From Gary North’s obituary for John Robbins:
Robbins first came to the attention of libertarians because of his self-published book, Answer to Ayn Rand (1974). He did not object to her defense of the free market. He objected to her epistemology, which rested on atheism.
I can see why he would think that, since for Christians God is at the level of metaphysics and ontology, in a sense prior to epistemology. However, while I can’t speak for Rand herself, for me at least my epistemology does not rest on my atheism. Rather, it is more the other way around. My atheism rests in part on my epistemological views (which inform and are informed by my metaphysical views, to be sure), but I (and I think Rand too) do not first assume God doesn’t exist and then develop my epistemology on that basis.