Go on then, I'm bite:
What is so bad about signing a player who we were legally entitled to offer contract to, with the fee to be decided by a tribunal that exists precisely for the purpose of deciding an appropriate fee for players who were signed without a professional contract? I mean, it can't be that immoral if there's a central body designed for that purpose.
It's hardly the same thing as accepting an offer and then going back on an agreement, is it?
By the way, I'm still very doubtful that Sheff Utd have done this, as it flies in the face of everything I know about contract law (as somebody else explained earlier). More likely that Sheff Utd haven't done this, but rather they are just trying to push the player towards Spurs (who made a better offer), IMO, and the press have embellished.