If you allow for caffeinated soda, where does it end? Because the next argument will simply turn into why is there no Starbucks in LES or on campus? I hear often on CB that BYU fans feel like we look weird to visiting fans by not offering them a caffeinated Coke. Sure, but even if we give them that, are they going to think we are any less weird when they realize they can't get a hot coffee on a cold November night game? Which many people consider to be much more healthy for the body anyway.
So it's a slippery slope issue I believe, so to avoid the coffee issue, which the church actually forbids, if I'm not mistaken, you might as well not get to that step by not allowing the caffeinated sodas.
That's my two cents.