A "meta-argument" against all future arguments for God's existence ?

[Jehanne]

As I recall he proposes one, and only one, "Noble Lie," at Stephanus 414b-c.

This is basically a founding myth -- sort of like "We all came over on the Mayflower looking for religious freedom" -- that Socrates felt would be useful for the unity of the polis. 

If you can find any other instances of Socrates recommending falsehoods I'd be interested to hear. He certainly never said that elites should lie with impunity to enrich themselves and harm others.

He may have told only one, but that lie would have had to be told and retold countless times and in countless ways for the Republic. If you take it literally, anyway.

He was definitely correct about the need for physical education.