If the science can be discredited, should the federal government really be using it to impose burdensome regulations onto the public?
There's a difference between "actually discredited, according to a reasonable person's opinion" and "'discredited' as an excuse for a biased person to ignore it." With this law, we're talking about the latter situation.
In particular, the Republican goal is to make the burden of proof for climate change so high -- by eliminating consideration of "non-reproducible" data, like all historical climate records -- that in order to be allowed to regulate greenhouse gas emissions the EPA would have to construct two full-scale artificial Earths, build a civilization's worth of polluting industry on one, and wait 100 years to see what happens.