re: A planet without automobiles
Maybe. But traffic fatalities are net fatalities, even with paramedic services. I only took into account those that died, regardless of emergency medical assistance. As insurance companies know, most traffic accidents involve young people, who might have had descendents.
If ambulances also saved old people having heart attacks they wouldn't have gone on to have children, so the net effect of ambulances on population is not something I'm going to speculate on. What would be your guess?