While urbanisation overall is probably a net plus for the environment, do keep in mind that, say, farming is quite area intensive. Someone needs to work at tho

While urbanisation overall is probably a net plus for the environment, do keep in mind that, say, farming is quite area intensive. Someone needs to work at those farms - and they are not going to commute to work by high-speed rail. (Granted, there are experimental urban farms out there, but I don't see those feeding the planet on a short-term scale.)