Horses and horse drawn transport generated an huge amount of horse poo and was a major health risk also horse riding is dangerous.

The comment was talking about the "danger" of mass transit, not horses.

I think it was mass transit prior to cars they where talking about.

There was a good period of time where trains, trams, and underground trains (from 1863!) were available as "mass transit", while cars were either not invented or rare luxuries. I don't think it makes sense to include horses in that.

How many pedestrian/car deaths are suicides?

I understand that overall mass transit is safer, but it still kills people. Without cars you'd have far more people biking, walking, etc and there are deaths associated with that.

If we switched to mass transit entirely and it saved 20,000 lives per year, the US death rate would fall from 2.74 million deaths per year to 2.72 million deaths per year. And our cities would become mega-metropolises, and crime rates would likely increase (killing a few more of the people we saved). I'm sure in that world there would be enough other bad side affects that a lawyer could write a similar document about the ills of mass transit affecting health, race relations, personal safety, etc.

And we'd give up a huge amount of persona freedom. Through out most of known human history anyone who wasn't rich was unable to travel more than a few miles from their birth place, without joining an army that is. The car opened up the world for everyone to travel anywhere in this country.