To an ignorant person, the greenhouse effect isn't simple. Not because the idea itself is complex, but because it implies we can and should do something about it.

And ignorant people would rather tell themselves it's not man-made because that would mean we can't fix it and, therefore, don't have to.

See Ian Danskin (if you haven't): https://youtu.be/dF98ii6r_gU

It's so ironic because we even have an inferno planet next door with a runaway greenhouse effect that everyone can use as an example. With an average surface temperature of 464 degrees, Venus got through to me as a small child. But knowing the type of ignorant person we're talking about, Venus would just be held as further "proof" that Earth's climate change isn't caused by human activity.

Two hundred years ago today, on July 17, 1819, Eunice Foote was born. Thirty-some years later, the amateur climate scientist made the remarkable discovery that when sunlight shines on carbon dioxide in a closed container—our atmosphere, for example—heat builds up inside. https://www.audubon.org/news/the-female-scientist-who-discovered-basics-climate-science-and-was-forgotten

And then there is also this:

A trove of internal documents and research papers has previously established that Exxon knew of the dangers of global heating from at least the 1970s, with other oil industry bodies knowing of the risk even earlier, from around the 1950s. They forcefully and successfully mobilized against the science to stymie any action to reduce fossil fuel use. https://www.theguardian.com/business/2023/jan/12/exxon-climate-change-global-warming-research