Hence "undetected".
You misunderstand. It's not that the individual is welcome to return, but that we essentially cannot prevent it. Take Public's Twin. He's a member we banned years ago called PublicSecrecy. In the intervening years between the two accounts, he must have registered upwards of 30 accounts here, mainly to say "Hahaha, you can't stop me" - whereupon he was rebanned. A few months back he registered as Public's Twin and PMed all the staff to say he was sorry and would just like to be on GTP again - he knows full well he's on permanent one-chance status, but he's still here.
Losing your original ID is the price you pay for your behaviour. If you value your online identity, you behave accordingly. Once lost, it's not coming back again - and no-one is ever going to use an account which describes the staff as "Y.O.U.R ALL A.S.S.H.O.L.E.S" (sic) ever again (notwithstanding the horrific Americanism from a guy from Tyneside).
At this point, we do not want THE HOG back in any guise - hence the instabans for the accounts he's tried to register since - but there is always the possibility he can register an account that we don't spot and blend in as a member of GTP society, following the rules that apply to everyone. If he does, we have succeeded in enforcing the rules, through turning someone who deliberately breaks them into someone how abides by them. If he fails to do so, we have succeeded in enforcing the rules by pruning those who do not believe they should follow them.
However, this isn't the appropriate place for a discussion of moderation standards. Please feel free to PM the admins (Jordan, Der Alta, Duke) if you wish to discuss policy, or stick a thread in Site Feedback (you're welcome to start it off by quoting this conversation between you and I) if you'd like a more public airing.