And he who is most skilful in preventing or escaping from a disease
is best able to create one?

True.

And he is the best guard of a camp who is best able to steal a march
upon the enemy?

Certainly.

Then he who is a good keeper of anything is also a good thief?

That, I suppose, is to be inferred.

Then if the just man is good at keeping money, he is good at stealing it.

That is implied in the argument.

Then after all the just man has turned out to be a thief.
And this is a lesson which I suspect you must have learnt out of Homer;
for he, speaking of Autolycus, the maternal grandfather of Odysseus,
who is a favourite of his, affirms that

He was excellent above all men in theft and perjury.

And so, you and Homer and Simonides are agreed that justice is
an art of theft; to be practised however `for the good of friends
and for the harm of enemies,'--that was what you were saying?

No, certainly not that, though I do not now know what I did say;