Fair enough. I personally would exclude all charities, all groups, all political parties, all lobbies, all organizations from ever flying a flag at a MLB game. No Gay Pride, no Cancer Society, no United Way, no NAACP, no US Army, no Heart Foundation, no anything!
Again, I'd have no problem with a Pride Day banner in the park. Heck, play YMCA or It's Raining Men during the 7th inning stretch. Have a cross dresser throw out the first pitch. Just no flag.