It isn't at all accurate to say that horses don't pollute. In some respects their pollution is worse.
In 1880 NYC’s population was 2 million. Today there are 23 million in the metropolitan area. We probably still wouldn’t have a good way of dealing with 25M+ pounds of poop a day. And at least garbage disposal is relatively orderly; horses just pooped everywhere.
Decomposing poop takes time, and it's pretty awful to be around while it's happening. Also, for something to decompose into the ground, it needs to reach the ground, which it's not going to do if the street is paved.
Of course, cars as the savior is also an oversimplified narrative, but it was a fun one.
To be short, saying that Bitcoin has the right of polluting while doing nothing useful in return because there are cars, is wrong.
