You cannot legally remove people from the subway for being insane. If someone is making me uncomfortable by regaling me with conspiracy theories and ethnic slurs, there isn't the clear legal authority to trespass them.
However, if one car costs $3 and the other costs $6, the person who is statistically likely to urinate on the seats is more likely to pick the $3.
I will honestly pay double fare just to sit in a car with others that can afford to pay double fare.