I don't think there is any free lunch here. The more trips that are made by car, and the longer those trips are, the more the community also needs to invest in

I don't think there is any free lunch here. The more trips that are made by car, and the longer those trips are, the more the community also needs to invest in capital costs like road and parking infrastructure (which also comes with a non-trivial opportunity cost in downtown areas). And the more you drive the sooner you'll have to replace your car, incurring more frequent capital costs. Of course alternatives aren't free either and sometimes they may not be worth it. But I disagree with the idea that it obviously doesn't make economic sense to invest in any alternatives once you've purchased a car.