This is a good video on how scientific consensus is challenged in the media.

This video compares the techniques once used to fight the scientific evidence that smoking is unhealthy with those now used to fight the scientific evidence that emissions of greenhouse gases are causing global warming and specific climate changes in many regions.

Of course, some people must be opposing the scientific consensus out of their beliefs that the science is wrong, but doesn't it seem likely that there is money buying the campaigns? Doesn't it seem likely that if companies and people who fund the effort to discredit science would lose money if people believe the science, that their motivation is not altruistic?

Policies should be based on prudent use of the best knowledge available, and the consensus of the scientific community based on peer reviewed research is very credible knowledge.