And eg cars used for Grab and trucks and busses are also privately owned.
More of the damage comes from all of the ways we arrange our lives so that we don't get hit by cars. Eg we don't let the kids out to play in the streets anymore.
Your proposal would be equivalent to dropping that number from 1 million to 0 million.
I think a reduction in the total number of cars is worth debating, but I don't think 0 is the optimal number.
Though I do wish Singapore would take inspiration from Japan, and eliminate street parking; and in general have the government exit the car storage business.