Not in any way defending them, but seeing how it doesn't break any of the FFP guidelines, it would seem to be a rather intelligent business practice. If,in fact, the Glazers sell the debt along with the rest of the shite that is united, as business people they've done rather well for themselves.
Not arguing with this at all, but I think the key point here is that they'll have done well for themselves, not for the club or the fans. It's not what ownership should be about.