Is Creon's feeling that he is guiltless in punishing Antigone persuasive?
Like just about everything else in this play, the answer is yes, and no.
Creon feels he is right to punish Antigone because, as the head of state, it is up to him to uphold the law, bring stability to the land and punish wrongdoers. And there's no doubt that, by burying her brother, Antigone has broken the law.
Or rather, she has broken the edict which Creon himself announced and set into law: that anyone who buries Polyneices will be put to death. The question is not whether Antigone has broken the law - it is whether the law is just. Creon is in a complicated position: he is the law-enforcer, but also the law-writer.
Moreover, Polyneices and Antigone are both under Creon's familial guardianship: he is their oldest surviving male relative. This means, that, paradoxically, burying Polyneices would be Creon's familial duty anyway: so whichever he does (buries him or punishes him) he's not doing one of his duties (as family member or as head of state).
Complicated! So Creon is guilty if you think that the law shouldn't have been enacted - and that Polyneices should have been buried: and not guilty if you think that the law was punishing a criminal against the state (Polyneices).