Wow, I do not see an issue with putting money on the games that you're not playing in. When ESPN, all of the NFL sanctioned talk shows talk about spreads and over/under, that's hypocrisy to the highest level right there. I'm assuming the stock market isn't off limits to Goodell and other owners and executives, right? It's not illegal for traders to invest in the stock market.
All that being said, I don't understand why you do it if you're an NFL guy, or any other professional athlete. Most people gamble to win money and try to get rich or even to win some money to pay their bills. I know I gamble to win extra money to purchase things I probably couldn't get on an every day basis, like say a watch or new wheels/tires, new golf clubs etc. When you already have all of that money, why do it? I could go cold turkey if I was worth millions. Money doesn't excite me when I have pockets full. Everyone is different, but I don't see the point in working so hard for your money, making enough to buy anything, only to gamble it away.