I put "pro-business" in quotes because, Republicans only pretend to be "pro-business." The reality is quite different. This came to me on reading about the Sinclair scandal (see the If Republicans are so good for business...).
Now everyone who's looked at the track record knows that markets do better when Democrats are in office, and anyone who's taken a look at the Conceptual Guerilla's website knows his view: that Republican conservatives favor "cheap labor."
But that's only part of the story, in my view.
The real answer is quite simple, which makes "cheap labor" a corollary: Republicans are "pro-business" because they simply can't run an honest business on the up-and-up.
They are incompetent to do so.
Proof? Look not only at Sinclair, but at Enron, Halliburton, Harken, Arbusto, Custer Battle, Edison Schools, Inc....