Commenter Anon69 makes the excellent point that by evading normal standards of criticism, Objectivism is "defenseless against rationalization":
In the final exam for the introduction to logic course I took in college, we were required to compare two passages, one from Descartes and one from Hume, and argue, first, that there was no difference in epistemelogical position between the two, second, that they manifested fundamentally different approaches to knowledge, and third, to give our own reasoned judgment of the matter. That is, we were to argue both sides of a position and then draw our own conclusion. More than weighing pros and cons, it meant striking forcefully against the position that I preferred. This was new to me, and I found that the benefit of that process was that it required me to neutralize my own feelings and tendencies in formulating the counterargument, which enabled me to proceed from a more dispassionate position than I otherwise could have.
Objectivist epistemology, as given in the rough-sketch ITOE or elsewhere, has no process or technique for such a critical examination of ideas, Rand's exhortation to "check your premises" notwithstanding. Objectivism is thus defenseless against rationalization. It sees no benefit from searching cross-examination. How could Objectivist epistemology justify such things as academic peer review or adversarial courtroom proceedings? It can't. In fact it survives by isolating itself from critique. When a process to take opposing argument seriously is eschewed, truth cannot be far behind.
For a philosophy supposedly devoted to reason, Objectivism's failure in this respect is breathtaking.