Good advice would be "so be particularly careful to check whether their arguments are logically sound and properly documented;" the original advice to skip past the quality of arguments and data to "so take their conclusions with a healthy grain of salt" is bad advice. The ad hominem fallacy isn't just unsound in principle, it tends to be pretty useless in practice. It can look reasonable at the time if there's enough groupthink, but would anyone like to nominate some cases where with two or more generations of hindsight we can agree that ad hominem arguments were a better guide to truth than simply addressing the technical arguments? And it can be wrong no matter how impressively much circumstantial evidence suggests that there could easily be a political motive: see, e.g., http://en.wikipedia.org/wiki/Robert_Conquest .
I wasn't saying their conclusions are automatically wrong, but merely pointing out that this one requires a little bit more scrutiny given the obvious political leanings.
It's like reading a science paper that questions something with a ton of evidence behind it. You just have to ask "really?" of all their claims before accepting it or rejecting it.
That there are badly motivated liars near a debate is not a reason to assume that everyone is lying or badly motivated.
Some random scientist is very (not completely, but very) unlikely to care much about the political implications of his results when analyzing his data.
A liberal politician looking to build his green credentials is likely to care a lot; as is a conservative Heritage foundation type.
But you know, sometimes science comes down on one side or the other. Science has shown pretty conclusively that nicotine is addictive; has suggested pretty strongly that humans affect the atmosphere in ways that affect how heat moves through water and air; and has shown pretty strongly that seeing lots of violence can be bad for children. Politicians from tobacco-growing regions, polticians from regions that produce fossil fuels, and politicians opposing limits on what should appear on television all therefore have the facts more or less not on their side; and unfortunately this usually leads to mendacity (of the sort the Heritage Foundation is displaying here) rather than any reconsideration of previously held beliefs.
