Modern cities are much larger than the continued use of horses would allow. So we would have more but smaller cities today if we still used horses. Alternative

Modern cities are much larger than the continued use of horses would allow. So we would have more but smaller cities today if we still used horses. Alternatively, is pollution from car exhausts, rubber dust, brake-dust, leaked oil, etc. worse than the pollution of thousands of tons of horse manure? Or not? Then again, today we spend billions on artificial fertilisers when there would be plentiful horse-manure to spread around instead. So cars versus horses is not such a simple argument. Did cars rescue our cities from horses? Possibly not.