>What if people refuse to use the train because it's scary, dirty, stinky, etc.? What if you could re-imagine trains where everyone can bring their own private mini-car and add it to the train? Then the car can be private, clean, luxurious, cheap, or whatever the owner wants. Would people adopt it then?

Because the "private mini-car" isn't as space efficient as just having one person. Space efficiency is a major point of public transportation, and the "scary, dirty, stinky" aspects can and have been solved in other parts of the world like Europe and Asia. What public transport advocates are worried about, I think, is that just like freeways, we are potentially going to create an enormous strain on the surface road system... the cars are going to have to come out of the tunnels some time, after all, right?

The reason criticism is warranted is because unfeasible, far out ideas like Musk's distract the conversation from proven and viable solutions and undermine their implementation.

Musk is providing ammo for persons that oppose public transit spending for political and idiological reasons that can be used in the political arena to argue to decrease public transit spending and slow down or stop implementation of public transit expansion.