Spirit airlines makes like 10% profit margin. Forcing them to absorb baggage fees isn't going to come out of their margins, it's going to come out of increases in base fare.

As to subsidies: you usually can't control whether you need the police or not. You generally can control how much you pack. My wife and I didn't even pack a check-in on when we took the kid to Disney World recently. Why should I pay more for people who have to have … whatever the hell it is that people pack in a checked bag for a domestic flight.