If the SCOTUS knocking down the freedom-removing portions of the bill was automatic, I'd agree with you. The sad truth is that it is NOT automatic--and W knows it. That's why thinking and rational Americans can't accept his signing it.
My thought from the beginning was that those who voted for this knew it was a rotten bill and figured that GW would bail them out with a veto. They really did not count on it passing.
Makes them look like they REALLY care about the issue and their vote would look good in the eyes of the voters.
Their plan was to make GW look like someone who liked 'illegal contributions'.
I think he decided not to be the fall guy and bail them out. As far as I can tell - it was a good decision.