I'm going to start this myself so I have a place to put my author's notes.
Consider these spoilers or points for discussion.
In the comics the Movieverse was derived from, Luthor was a true Nietschean genius - He really was brilliant and considered laws and morality to apply to lesser beings.
In the Superman movies, Luthor is brilliant, but he's also a blowhard who assumes everyone will bow to his wishes. In Superman the Movie, he plans to nuke the San Andreas - and does so. But he fails to consider the response of the US government or even the surviving locals - he's planning on building on 'his' land without any thought about whether or not he can hold onto that land without an army? He's going to try to have the rest of the world respect his ownership of the land once the world figures out what he did? He thinks someone with a rifle won't take him out the first chance they get?
We're not talkin' fool. We're talkin' damned fool.
In Superman II he's trying to negotiate with beings who not only don't care about anyone but themselves, but don't need him - still he betrays the one person who could get him out of the problem he's gotten himself into?
In Superman Returns, unless the new continent had food replicators, he's dug himself into a major hole - if he succeeds in flooding the world according to his map, the US still has military capacity that will cheerfully drop nukes on his head. Even if he manages to create an anti-missile defense, THERE IS NO FOOD ON THE ISLAND! There is no topsoil and he's just flooded everywhere that he might import it from.
And there's no guarantee that the Kryptonian technology will work properly in the presence of kryptonite. Given what we know of the delicate nature of high-tech, I wouldn't bet on the technology he's counting on to work while exposed to high levels of radiation (solar OR kryptonite.) There's also no guarantee that kryptonite is not harmful to Earth life forms in the long term.
That's my reasoning. So enjoy the ride.