"Would the defenders of Jack Phillips of Masterpiece Cakeshop call it his First Amendment right if he refused to bake a wedding cake for an interracial couple?"
Spot on, Cheryl Kasson!
"People used religious arguments to support their opposition to interracial marriages" But the US Supreme Court shot down those arguments.
The US Supreme Court also shot down arguments by bakers and flower arrangers and wedding designers who insisted their religious and artistic freedom overrode state laws banning discrimination based on race or religion.
Religious conservatives never had a problems with civil rights laws and court rulings upholding them -- until gay people and couples began being included in state civil rights laws.
This is all about religious conservatives wanting government, through the courts, to protect their right to show superiority over gay people. Religious conservatives want to be protected from discrimination while discriminating against gay people. This is all about power.