Republicans are big believers in the market. Governmental regulation is to be avoided at all costs, and the more regulation eats into the bottom line the more likely it will be decried as being too "burdensome" to industry.
Market forces, however, do not favor kindness to the environment in American-style capitalism, which is focused narrowly on short-term profits over long-term viability.
We all want a nice, clean environment, but the truth is we all secretly hope the other guy is going to be the one paying for it. Given a choice between a shiny new SUV and the latest electric car, Americans choose the SUV. And we will continue to do so until the electric car is at least as good and as cheap. Americans aren't getting fatter by the year because we don't know that Twinkies aren't as good for us as celery sticks, but because we want the damn Twinkies and decide we'll pay the price later, if at all.
Environmental regulations are like your Mom's rules-- you know they are there for your own good, but you would probably not follow them if you didn't have to. Republicans by and large think we'll do fine without all the rules. People are nice and do the right thing usually, right? Then again, Democrats aren't exactly charging to battle waving a Green banner these days either are they? They've copped to the fact that most people really want the Twinkie, and they don't like being told they can't have it or have to pay more to get it. While individual Dems may be green, the party as a whole is rather apathetic over the issues unless they can find one like drilling in ANWR that is guaranteed to get good press.
All that being said, there are certainly extremists within the environmental movement who do not seem to be able to come to grips with the fact that we cannot exist on this planet without making some environmental impacts. These folks are as damaging to the cause of environmentalism as anything occupying a chair in the Capitol. The image of environmentalists as whacked out tree-hugging eco-terrorists who want everyone to subsist on tofu and rainwater doesn't help real environmental issues gain much traction in our esteemed legislature.