Oh my word, I appreciate it's not the greatest injustice in the world but I'm afraid I see this as utterly farcical. I think presenting it as a 'discount' is totally disingenuous too since the practical reality is a two-tier price system based on an arbitrary trait. I can accept price variations that help oppressed or disadvantaged social groups but that's not the dynamic here, it's the opposite of that. This is somebody belonging to a powerful social group using the enhanced power of a business to penalise people that don't conform.
As for any arguments about it being their business so they're entitled to it, I tend to reject that perspective as neo-liberal callousness that washes its hands of consequences. I don't think society should abdicate its duty to ensure justice and leave people to the fate of the magical market, that just allows existing inequalities and bigotry to be entrenched. Equally, a business is not a person or an extension of a person to me. In my mind, it is a separate legal entity participating in the public realm with greater power than a single individual and must be regulated to a greater extent to prevent unacceptable power disparities.