Heh, you're right. I suppose I didn't specify sufficient criteria.

I think that philosophers who have stood the test of time have already undergone post-hoc feedback. Aristotle, Nietzsche,Hume etc all had areas of faulty reasoning, but for the most part this has been teased out and, brought to light, and is common knowledge now. All of them were also exceptionally talented and gifted, and made better arguments than the norm. The fact that their work HAS stood the test of time is an expert vetting process in itself.

In terms of a random philosophy professor on the street, they haven't gone through this process of post-hoc feedback to nearly the same degree, and likely haven't gotten enough real time feedback to have developed these sorts of rationality processes automatically. Singer perhaps has had a bit more post-hoc feedback simply because he's popular and controversial, but not nearly as much as these other philosophers, and I suspect he still has lots of faulty reasoning to be picked up on :).