I don't agree it would have been seen as treachery -- it would have been smart. Why not simply say, "Hey, Tarkin, why don't we go and check that the Rebellion is actually on Dantooine before we destroy any leverage we have over the Princess?" I doubt Leia would have held out, truthfully. And then they would have used it on Yavin. At the very least, he could have tried. Or, if he hates the idea of the Death Star so much, why does he participate in Leia's intimidation during its destruction? To me, his complicity is clear and I don't get why it's so often swept under the rug. If there was only one crime I could undo in the Saga, it would most definitely be Alderaan's destruction. Unless there was something I could undo to stop Palpatine from coming until power in the first place, for certain, of course.