The US has laws prohibiting Housing discrimination on the basis of race (and other things).
Why are cakes different from housing?
When I renew my real estate license every 44 years, I have to re-study the federal and state laws, prohibiting discrimination in housing.
If a black (or disabled, or homosexual) prospective client approaches me, I am prohibited by laws, from refusing to serve them. Further, landlords and sellers, are prohibited from refusing to sell to various categories.
California's law dates to 1959, and the federal law to 1968. Both now include sexual orientation.
Housing is a much bigger deal, than cakes. If you own a house/apartment for rental you are obligated to not discriminate against gays.
This prohibition is even in effect, for property owners that have a religious belief against homosexuality.
Cakes and bakeries make for nice visuals, but real estate is a bigger part of our national and community lives.
I am fairly neutral, but my point is to say cakes are only one aspect of equal rights/non-discrimination for minority categories.