They argue against it due to the long, sustained campaign of anti climate change propaganda peddled by people who profit massively from fossil fuels. Exxon acknowledged climate change and the fact that their products were a contributor...then planned, funded and actioned a campaign to make people believe it was all possiblies and maybes. Obviously it has worked to some degree, as people still refute it.
More here: https://www.ucsusa.org/global-warmi...fossil-fuel-industry-climate-change-deception
Genuinely frightening.