That's a nice substantive reply.
"[Atheists] do believe in scientific determinism -- the unbreakable sequence of cause and effect, and that is predestination. It is the assumption all laboratory workers make and it rules out free will. Any present state of fact, any action taken, is the inevitable outcome of a series of events going back to the Big Bang that produced the universe." Jacques Barzun, "From Dawn to Decadence."
Where is the flaw in this? It seems to me to be a far more demonstrable truth than Rand's "objectivism."
And I don't see how quantum physics and the randomness therein invalidate it, because quantum physics has no application beyond the sub-atomic level.