Socrates' questioning of Meletus has led Meletus to assert logically inconsistent statements:
(1) Socrates corrupts the youth intentionally.
(2) Nobody intentionally harms himself.
(3) People who corrupt society ultimately harm themselves.
If (1) Socrates corrupts the youth intentionally and (3) people who corrupt society ultimately harm themselves, then (2) must be false (which is ridiculous.)
However, if (2) nobody intentionally harms themselves and (3) people who corrupt society ultimately harm themselves is true, then (1) must be false (since Socrates cannot be corrupting the youth intentionally). If that is the case, Socrates needs to be instructed on how his activity is corrupting the youth.
Socrates concludes that he either does not corrupt the youth or else he corrupts them unintentionally.