What's more, by targeting the effects, not the cause, you're helping create a better, free-er world, where governments aren't dictating how people live their lives. If the desired effect is "less global warming" (and you implement that via a fair CO2 / CH4 tax), then people can choose how they're going to reduce their CO2 impact. Maybe I prefer to eat 1 steak per week and cycle to work, whereas my neighbor eats soybeans whole year round and drives around in a car.

Finally, by taxing (not banning) undesirable externalities governments spur technological development - people/companies can invest money into figuring out how to get the same result ("eat steak") with less of a climate impact (e.g. by feeding seaweed to cows), resulting in a win-win.