I don't think self sustaining subways are a good thing. You want tax subsidies on ridership to bring the price really low, to enable as many people as possible

I don't think self sustaining subways are a good thing. You want tax subsidies on ridership to bring the price really low, to enable as many people as possible to use it as often as possible. Profitable infrastructure defeats the purpose of infrastructure, which is to be a force multiplier on others productivity. Introducing profit motive diminishes the potential effectiveness.