Well, not everybody drives alone. Moving one person in a car emits comparable amount of CO2 as a person going by foot and moving only two people by car emits less CO2 than moving those two people on foot. We should discourage driving alone, or driving extremely short distances, but not discourage driving cars in general. Cars are surprisingly more energy efficient than walking/cycling if utilized fully. Also a big car fitting 8 people is more energy efficient per person than a small car that fits 4 people.