People, get off your soapboxes about "Big Brother" and what this country is coming to with regards to personal responsibility and individual liberties. This has absolutely NOTHING to do with any of that.
The NFL is a privately owned company choosing to tweak an operating policy at their venues out of the owners' prerogative to do what they want to maximize profits. What could be more American than the unchecked exercise of the free market?
It's not even really an issue of liability when it comes to drunk driving. That might be a contributing factor, but the primary reason for this policy change is their attempt to dictate a less rowdy, more family-friendly gameday environment, because those are the kind of fans you make the most money off of.
Think about it: your typical die-hard, tailgating oldschool football fan brings their own food to the game, their own alcohol, already bought their Pats jersey/sweatshirt/hat, etc. a couple years back, and if they weren't at the game, they'd be at home watching the game on TV.
They've already gotten a lot of the money they're going to get out of this guy, so all they get by having an entire stadium full of them is seriously increased costs when it comes to security, cleaning and maintenance, and traffic control.
Now, not only are drunk people are a LOT more expensive to deal with, they also tend to shock + frighten other patrons who present many more profit opportunities. You ever see parents with a bunch of little kids at games? The kids are usually walking around with armloads of the various souvenir crap their parents have bought them to keep them quiet.
Then they have to buy their kids the over-priced hotdogs and fried dough, and with all the stress they're under, what the heck, they'll indulge in a glass of premium-priced beer or wine. Of course the kids still get bored 3 times during the game, so the parents have to take them around to all the various alternate entertainment opporunities the new stadiums have, thus feeding that revenue stream.
Face it: as long as the NFL is the most popular sport in the nation, it's just better business to keep a revolving door of parents + dilettante yuppies coming in and out of their stadiums, buying crap they don't need, and requiring half the crowd control.