Why do so many global warming deniers feel compelled to write their own truths?

Honestly I don't think most of them are creative enough to write their own truths. Though they may be saying things that are completely false (e.g., volcanoes emit more CO2 than humans), I would be willing to bet that someone first told them those arguments and they are just repeating. It's not like there is any shortage of disinformation on the internet and radio.