Moderation Enforced

Being humorous doesn't make him trustworthy. Or a good person. or a decent person.
How pleasant you found him is irrelevant. He broke rules. He was removed. He continued to break rules trying to bypass his own removal. Your personal feelings have no bearing here.

There are no personal feelings in moderation.
I believe we've covered that.

We kind of shifted to discussing his personality for its own merit at one point:

Because clearly he's an honest, trustworthy person who can be taken at the value of his word.

The argument at work here is that the rule, given that it was erected against an individual, is no longer necessary or even appropriate if said person is no longer going to commit the crime. The counterargument obviously would be that it is necessary on grounds that the person cannot be trusted for his words.

Locked is appealing to his anecdotal experience with the individual which, in all fairness, should not be taken for its justificatory merit. If we, however, grant him the benefit of the doubt, we can agree that the rule is now obsolete.

On the other hand, there is every reason to question the personality of the offender given what we have been shown, yes. The decision, therefore, is whether or not Locked's testimony for this person, supported by their daily communication, can be given confidence. In my opinion, the weight should be given to his side lest we be arguing from ignorance.