It's not just Republicans.
You might also want to ask why many independent and retired scientists not dependent on government sponsored research for their livelihood also oppose the theory of global warming and the shenanigans exposed by "climategate".
In true science you don't hide and withhold the raw data from other scientists who would like to verify findings. You don't plot and scheme to prevent scientists that don't agree with you from being published. You don't alter and "homogenize" data such as James Hansen does with GISS data at NASA to exaggerate the warming. You don't say the "science is settled" before doing any research into the many warming and cooling cycles, including ice ages that have been occurring for thousands of years.
You don't make wild statements and use scare tactics in order to get media attention as they did in 1988, predicting a 20 ft rise in sea levels by now. ( Noted oceanographer Nils-Axel Morner states that sea levels have risen very little in the past 50 years).
While they dwell on the melting of sea ice in the Arctic ocean, which actually stopped three years ago, they fail to mention that the icecap in Antarctica, which holds 91% of the World's ice is getting thicker!