They say that the wise and thoughtful man keeps to himself. Does that mean that philosopher as Plato and onward have been inferior minds?
The four sophisms / denials of Gorgias:
1. Nothing exists;
2. Even if something exists, nothing can be known about it; and
3. Even if something can be known about it, knowledge about it can't be communicated to others.
4. Even if it can be communicated, it cannot be understood.
These are sophisms because they contradict themselves. If the Jew is right and "he who knows, doesn't say; he who says, doesn't know", he shouldn't have said anything.
Plato got a lot of his teachings from the hermetists in Alexandria and was seen as treacherous for giving away the esoteric knowledge to the profane. So yes, he actually did the world a disservice by leaking arcane secrets to people who weren't ready for them, since the correct tools in the hands of the wrong man yield incorrect results