Of course if we had no affiliation to the Spurs franchise, it would be easy to say, oh wow, Howard has many good years ahead of him and is a dominant defensive force. Who knows how long Duncan can still play, this trade would be good.
But first of all, there is the loyalty. As someone that's been a Spur his whole career, it would be slighting Tim Duncan, one of the greatest Power Forwards of all time, to trade him. Second of all, we just built a team around Duncan that has a shot to win it, I think everyone would prefer to see how it plays out next year. Finally, this hypothetical is about as likely to happen as trading Bonner for Pau Gasol, so of course your post is being treated lightly with homerism.