Okay, "major harm" was just the first thing that came to mind...
As has been pointed out on this and other threads, SWA starts with a low-ball price, but will raise it over time.
Do you actually think that eight flights a day for connecting flights will push Northwest/Delta out of MSP??? Remember, that $69 fare to MDW is sans fees and taxes... and only to MDW (and don't forget that not every seat is that cheap). Wanna go somewhere else? Well, it'll cost you more money. SWA connects to more than 50 cities from MDW... how many cities does NWA fly to non-stop from MSP?
Don't get me wrong, I'm a free-market/consumer's choice kinda guy, but gimme a break, this is hardly doom and gloom for NWA.
Yes, I guess I have a dog in this fight, but I don't see SWA being a threat in MSP.