It's hard to argue against his abstract proposition since he didnt really provide an alternative plan, but in general, there are two main factors I'd like to stress.
The first is the loss of mobility and its results. One almost universal facet of the alternatives to cars that people suggest is that they limit where you can enter and exit the system. You can't use a train to navigate to anywhere you want to go: you use it to get close and then use some other way of getting the rest of the way. Remove other transit systems, and this will effectively set property values. Want to open a store? Well, if you're an established player with easy access to capital through the investment bank that handled your last merger, than the cost of leasing or purchasing property with reasonable access via transportation is fairly easy. But if you don't, you're probably not going to be able to afford that. You're going to have to locate yourself in a far less accessible location. And the value proposition of your business now has to overcome this difference as well in addition to regular value you would offer. From a consumer standpoint, this means you have fewer alternatives. Things have to be pretty bad with your existing supplier of a good or service for you to switch if doing so is going to entail a higher inconvenience in terms of access. I saw this all the time in Chicago. People could charge a premium beyond what their higher rent would require simply because they knew that you would be reluctant to walk another 15 minutes to get to someone who was charging 10-20% less per item.
There are additional fixed costs that would go with the logistical concerns a model like this would entail. How are you going to get things to and from your business? The constructs are going to most likely favor established methods. Say we don't allow cars to drive, but we do decide that we need the infrastructure to allow 18-wheelers to get through, and you can use that method instead. Well now you need a loading dock. Now you either need to pay someone else a premium for hauling it for you or buy an 18-wheeler yourself. You can't simply use the car you were already using to commute to your day job while trying to start this new business. You can't sacrifice additional time to lower the cots. You are effectively confined to hiring other people to do it for you because of the system.
In short, it makes the system much more rigid. It leaves fewer feasible alternatives both for the consumer and the provider. It also makes barriers to entry far higher.