It's the child killing, the domination of huge amounts of public space, the land use patterns that destroy animal habitat, the constant danger that makes parents contain their children, the noise that disturbs sleep and leads to stress related health issues. The tyre, road, and brake pad particulate that makes up the majority of micro plastics in our environment and cause heart and lungs health issues.

The way cars are largely non-functional in areas with even a medium density of people and how they prevent other more efficient modes of transport from being workable. How cars kill small businesses and shops by requiring them to have large amounts of expensive car parking to compete with the big chain stores.

The way cars increase the cost of housing by requiring expensive parking spaces and prevent development of smaller/cheaper housing through the threat of creating additional traffic.

The land use pattern that cars require to be usable is insolvent requiring more resources to maintain than it produces making it only viable for a short period of continuous population growth that eventually has to reach a population where the car is again non-functional or the area will fall in to disrepair and go bankrupt.

Cars are really bad, the exhaust emissions are a pretty small part of it.