A big assumption here is that GWB's reasons are rational.

I prefer the interpretation by Doug Wead, who wrote "All the Presidents' Children" and who used to work for GWB back when his father was president. (I saw him on CSPAN "Book TV" last weekend.)

He says GWB is simply trying to finish his father's unfinished business.

The two biggest failures of Bush Senior's administration was that he failed to keep his "no new taxes" promise and that he failed to get rid of Saddam.

Therefore, under Bush Junior's administration we get tax cuts (for the rich, mainly) "whether we want them or not" and we have a war for the explicit purpose of getting rid of Saddam. It doesn't matter what the other results will be.

In short, Bush Junior wants to make his daddy proud of him.