Spirit's customer base still needs to fly and they're going to find some other airline.
Not exactly true. Spirit customers fly because the price is affordable, not because they must fly. There may be some customers that must fly, but they will not be the type that gained Spirit’s reputation as ghetto air.
Just like Carnival cruise, they are known as ghetto cruise line because they lowered the price. That drew low class customers. If they raised the prices, that would not necessarily mean all the ghetto customers simply transfer to other, more expensive cruise lines. It’s not a necessity, they simply would stop going on cruises.
Alot of Spirits customer base may fly because it’s affordable, and only because of that. It doesn’t mean they must fly.