Two problems, both of which have already been discussed.The "Pooky Gurantee" has never been broken and Pooky definitely won't lie when giving such a gurantee.
It'd be unethical to use such a device if I was FORCING people to believe me, they have their own wits and they can use them to evaluate whether my gurantee is valid or not, in all my games I've never guranteed and been lying at the time of the gurantee.
If BJ/Fritz/IS can play games and not give reasoning for votes and use metagaming(they'd do it protown or antitown) to keep people from voting them on no logic, why shouldn't Pooks be able to using metagaming to convince people that he's protown in a game?
It took time to build up such a long reputation and record of honest gurantees!
1. If you have a reputation for being honest with such guarantees, then in a future game as scum it will be your "best play" to lie and give one. By refusing to do this when it is best play in a game, you are sacrificing best play in the current game for future benefits, which I have problems with. The example of "keeping people from voting them on no logic" is not analogous, since that generally *is* best play. That isn't to say that those you mentioned do always play for the current game rather than the metagame, but such examples don't excuse this, they just mean it's a more widespread issue.
2. Making a statement like the start of that quote constitutes talking outside the game. If you were to make one of your guarantees in the future in any game you are currently in, I would say this would qualify as breaking the rules of that game (assuming the rules are standard); and even having it out there for future games is questionable.
Clearly there's an issue here about discussing things that might affect future games; if we can't say what we might do in a situation because it may compromise things in the event that situation comes up, we'll have a hard time talking about anything. But I have to draw the line at making statements with the sole intent of influencing future games in your favor.