Hmm. At first, I was inclined to agree with you. But the more I think about it, the more I suspect that Plato and Aristotle may have had a net negative effect on humanity, if only because they were too awesome. Placing philosophy's heavyweights right at the start of its history might well have discouraged a lot of philosophical diversity, particularly since it occurred at a time when antiquity was so central to authority. This is more the case for Aristotle, since he expressed less confusion and unclarity in his arguments. But unclarity can also have a stultifying effect, as shown by Christianity and, more generally, Neoplatonism.
If there weren't a lot of other philosophers at the time (including three other schools independent of Plato/Aristotle that were also founded by students of Socrates), I'd be more inclined to agree. But it's not clear to me that the course of philosophical history needed someone as amazing as Plato or as Aristotle, at that point in time. A slower development might have been healthier.
But given that philosophy just didn't really emerge elsewhere, it seems like it's a pretty contingent fact about human beings. If it weren't for Plato and Aristotle, there just might never have been anything like it at all. And then what the hell would we do with our time?
Since LessWrong is a major congregation point for certain philosophical ideas, and because people here tend to be more objective (in the sense of not being self-deluded) than elsewhere, I thought I'd ask people's views.
To be clear, by "Greatest Philosopher" I am referring not to the most correct philosopher in human history but the one who deserves the most credit for advancing human philosophy towards being more true.
Off the top of my head I would say that a prime candidate would be Hume- amongst other things he rejected the idea of a soul, realised to a much greater extent than his predecessors the limits of human knowledge, and opposed the idea that reason is somehow an objective force that can make priorities independent of emotions.
Aristotle deserves considerable credit relative for his time but doesn't make the list because although it wasn't his fault his ideas were dogmatically accepted and held back both science and philosophy later on.
Your thoughts?