The first one would say:

no they definitely all have to have their own engine, because they should have the freedom of choice. Trains are authoritarian because they only allow for one route.

Which then leads to
But they're all mainly travelling the same few routes

Yes, but they should have the freedom to choose other routes

So you want to build highways everywhere?

Yes! Or no, not really. Just highways for the main routes people travel.

That's just rail lines but worse.

No it isn't, people can completely decide where they want to go themselves. We're gonna have offramps at major clusters of traffic, you know where a lot of people get on and off the highway. And then we're gonna have less heavily dedicated roads for smaller traffic.

That's just light rail, you're describing light rail. Are you going to asphalt the entire world?

No, there's not enough money in that.

So you still decide what routes people can take. Whatever, this "road"system will require immense resources to maintain.

No it won't, there's not enough money in maintaining public infrastructure. We're going to let things just sort of... decay. Maybe we will sell off some major nodes to private companies that can then charge outrageous amounts of money for using the road.

Will you use trains for anything?

Yes! We will use them to transport toxic chemicals.