If you want to get intoxicated at a football game using "booze," you are going to have to buy said booze from the NFL concessionaires, at hefty prices and with a decent profit to the concessionaires and the league.
It's a business decision, first--anyone smoking pot isn't buying beer, so it's cutting into their profit. They aren't running a charity. Anyone stupid enough to spend the crazy mad money to buy a ticket to one of those overpriced sporting events needs to understand they have to spend even MORE money to eat food or drink beverages inside the stadium. It's their house, and their usurious rules. You don't have any "rights" that they don't afford you, and your option is to stay home and turn on the tee vee.
Second, it's a public perception issue. Pot has a distinctive smell, and parents with children at the game, who are anti-weed, might get highly offended and upset if they smell that shit on the wind.
They have the right to limit what can be consumed in their facilities. People who don't like it can stay away. I can tell you right now, it is more likely that I will dance lead in the Bolshoi Ballet than ever attend an event at Coor's Stadium, so I really could give a shit either way.
That said, if these two aspects--the business decision aspect, and the public perception aspect--are ever mitigated, what you will see happening at Coors Field is that anyone wanting to do a little weed will have to go to a cafe on a mezzanine, buy some overpriced herb, smoke it in the NFL cafe, and then return to their seat. The folks at Coors Field are gonna get their cut--no "bringing your own from home" allowed.