In the case of the Gay's buying tickets to Six Flags, the problem is that the park does not disclose this information to the public. You may say that it is not the parks responsibility to tell the public, but it becomes a problem for families who have come in some cases from out of state to enjoy the day at a 'family' park.
If the Boy Scouts buy a bunch of tickets to the park, the marquis outside will say 'Welcome Boyscouts' or something nice. There is no big sign that says 'Welcome Homos' because Six Flags doesn't want to scare of the family clientelle. So this family from out of state buys their tickets (at almost $50 a piece full price) and goes inside the park. At some point little Jenny asks 'daddy, why are those men holding hands' and daddy starts to take a good look around him... by the time he figures out what is going on, it is too late. He has paid his money, redeemed his tickets and there are no refunds to be had. He can suffer the rest of the day at Six Flags over Sodom, or be out of pocket for the money he paid to show his family a good time.
Protesting at the park is primarily to warn families about what is happening that day. Many of them turn around and express their gratitude for the warning.