Assuming the goal is to provide mass benefit, then if an idea has to be subsidized, then it's probably not a good (economically viable) idea. Of course if the goal is wealth redistribution (stealing from people under the false agenda of helping) -- then subsidies are always rationalized. Mass transit is an example of the failures of public policy. While they sound good in concept, when you look at how much money they lose, and thus have to take from taxpayers to exist, they are disasters. Here's some examples.
Mass Transit : 3 items
Roads and Infrastructure - Many view the United States as a free market capitalist state and Nordic countries such as Sweden and Finland as socialist due to their extensive welfare system. Yet, in the United States, most roads, highways, and other transportation infrastructure are publicly owned and operated. Meanwhile, the vast majority of roads in Sweden and Finland are operated by the private sector and maintained by local communities. The Norwegian model works better and costs half as much. In the U.S. it also helps to remember that the vast majority of roads were created before the federal government got involved in national highways, and they worked just fine... often better, and definitely much cheaper and with more local control and less waste. People that love big government can never reconcile this reality with their imagined world where Government makes things better.
Light Rail - In a vacuum, Light rail sounds great: trains are efficient, comfortable, and just fun. But we don't live in a vacuum. In the real world (a) they cost billions that could be better spent on roads/busses, so that hurts fares and the poor (b) they are less convenient than busses with fewer stops/routes means more time to get door-to-door (for most people) (c) more mass to stop and start, fewer riders and cutting through traffic (more traffic/idle time) results in more pollution (d) they pull riders from more efficient busses (not cars) and thus increase pollution even more. So other than it cost more, serves fewer people, hurts the poor, requires state subsidies (loses money), and increases pollution, they're a great idea. Supporting them is anti-environment, anti-economics and anti-science.
Carpool lanes - These monstrosities cost California $2.5B+, to get a 20% capacity loss, which increases pollution, a decrease in carpooling, and 50%+ increased injuries (both accident frequency and severity). It turns out a high speed lane right next to a parking lot increases accidents and injury on entry/exit, and not allowing drivers to use the entire road only decreases traffic flow from optimum. Supporting them is anti-environment, anti-economics and anti-science.