Original sentence: In Moore's discussions with various people – including South Park co-creator Matt Stone, the National Rifle Association's then-president Charlton Heston, and musician Marilyn Manson – he seeks to explain why the Columbine massacre occurred and why the United States has a high violent crime rate (especially crimes involving guns), and promotes the opinion that such crime in the U.is relatively higher than in other developed nations
Edited sentence: In Moore's discussions with various people – including South Park co-creator Matt Stone, the National Rifle Association's then-president Charlton Heston, and musician Marilyn Manson – he seeks to explain why the Columbine massacre occurred and why the United States has a higher number of violent crimes (especially crimes involving guns), and he demonstrates that the occurrence of violent crimes in the U.is relatively higher than other developed nations