It's because the fare and boarding latency on planes is much higher, which funds the cost of having security guards around and amortizes the check-in time penalty.
Maybe. But in any case, you don't need to re-invent the wheel to check that passengers on busses and trains pay their fare. Just learn from any of the countless successful systems around the world today, or in the US's own past: streetcars used to be widely profitable, and that only worked because they actually managed to collect fares.
(Careful: I'm not suggesting that collecting fares would make streetcars widely profitable again. I am merely suggesting that whatever mechanisms they used to enforce fares can be learned from.)
It's a tradeoff you can make. The US is far from the only country in the world where fare evasion is a problem. I've lived in countries with similarly high inequality and homelessness where fare evasion was such a problem despite enforcement that the bus drivers would simply refuse to pick up certain passengers, and conversely people would then hitch a hike on roller skates behind the bus.
I don't doubt that there are countries worse than the US (in this regard). But that doesn't mean you can't learn from the success stories. Especially since they are really common in a variety of places that don't have much in common otherwise, so it can't be too hard to clamp down on most fare evasion.
> [...] and conversely people would then hitch a hike on roller skates behind the bus.
I assume there's not much overlap between the really problematic passengers (often loud, drunk, aggressive and/or mentally ill) and the skaters? Mostly just because you need a minimum level of physical fitness to pull this feat off, and you need to be organised enough to both have skates and have them at the ready?
In most places I lived in, the traffic police (if nothing else) would nab you for trying to pull this stunt.
