I thought that most businesses reserved the right to refuse service to anyone without giving specific reasons....or does this only apply in certain circumstances??
They have that right, so long as the reason for refusing service doesn't violate anti-discrimination laws. A shop can refuse service, for example, because someone is barefoot because attire is not covered by the laws. They cannot refuse service because someone is Muslim because religion is protected. In this case they can refuse service because the customer is gay because sexual orientation is not covered by Missouri anti-discrimination laws.