One of Thomas Sowell's principles of conservatism--- what he calls the constrained vision--- is that while leftists believe in total, free lunch solutions i.e. "we will eliminate poverty--- forever!" conservatives believe in incremental approaches to problems that seek to gain gain a net benefit, recognizing that any approach will have costs as well as benefits.
The cost of not electing Republicans is electing Democrats. To think that simply because Thomas Sowell criticizes President Bush and the Senate he doesn't care whether or not the Senate remains Republican would be a unwarranted leap of breathtaking proportions.