You know that saying about statistics? Yeah, it can apply to scientists, too.
It's not so much that the science is tainted, but rather the interpretations and causal relationships that are attributed to it. Climate change isn't like counting fruit fly mutations -- we have very limited data to work with, and the extrapolations from such limited data can easily be flawed, influenced, or otherwise wrong.
That said, I can't respect the people who somehow "think" that 7 billon humans, billions of cars, and trillions of tonnes of shit from industrial plants has had no effect on this tiny, fragile planet.