Sorry, but it is not as simple as that.

If you go to a movie, a play or a concert - you are paying to watch a performance. You are giving the performer the opportunity to present their art - AND their views. What you take away from it is your choice. Your level of participation is up to you.

A baseball game is not a public event in the sense that people pay admission to get in and they are subject to rules and regulations for the event.   A public gathering would be a public park or city center. A ballpark is owned and operated by a specific corporation. You don't have to be there if you don't want to. Ask for your money back if you are offended, but don't sit there and say it is an imposition. You put yourself in the seat and if you get hit by a foul ball or "God Bless America", the choice was yours.

I think there was anger over this for the same reason I stated above. Those fans are not different from those they are protesting against.