This is a refusal to participate in a process explicitly designed to make it harder for people to assert their Constitutionally-protected rights, by arranging s

This is a refusal to participate in a process explicitly designed to make it harder for people to assert their Constitutionally-protected rights, by arranging such that there's nobody to take to court to protect those rights. That's how it's different. The cake-purchaser is not a government trying to use the cake as a shield against civil rights litigation.