As I understand it we are unable to return this bloke because Iran will not accept their own people back.
After he's done his time, what do we do with him? You say "it's a little more difficult". Well duh!
You would simply happily release him into the community, I guess? Give him welfare, a home and a job - and then let him bring the rest of his family over?
In the meantime he has cost the Australian public a fortune in detention costs, legal fees, gaol (presumably) and welfare. All this for a criminal and (it seems) a paedophile.
Great! Just great.
This is one of the reasons why we need strong border protection laws; we do not need potential criminals arriving leaving us in situation that is a fait accompli.
Prevention is better than cure, as they say.