[mathgeek]

It could be seen as pro consumer, but it also could be seen as anti competitive. Spirit going under would open up space for a new competitor to potentially move in.

An analogy would be two competing gas stations at a very busy intersection with no plots nearby to build more stations. Just by existing they either drive each other down on price or collude on it. One going under means a new station could exist, but one buying the other guarantees prices do not go down.