I think I'm right in thinking that cars are responsible, in a developed country, for about 10 to 12% of CO2 so by far from being the biggest culprit (other transport brings that figure up to 20% or more). The beef and dairy industries probably dwarf that (don't have the figures though).
The Aussie Petrol Head John Cadogan is interesting on this. He fully accepts man made climate change and that it will eventually lead to ecological collapse. He think climate change deniers are morons who simply cannot accept science. He is, however, a huge critic of EVs, especially in Australia where they will, effectively, burn coal. The general point is well made though - cars are not the biggest culprits.