Freedom of assembly is also a form of freedom of expression, one that is also constitutionally protected. People have a right (within reason) to refuse to do business with other people as a form of expression. See the Mozilla/Brendan Eich situation as an example of this.
If a restaurant owner kicks you out of a restaurant, he is also expressing himself, just through association instead of speech. Additionally, he has property rights to consider. He is allowed to control the operation of his building and business. On the balance, the restaurant owner should be favored in this sort of dispute.
Why involve the cops? It's not strictly necessary. In many cases, there are private citizens that do the same job (event security, bouncers). But the cops, at the end of the day, are enforcing the the restaurant owner's rights to property and free association. The enforcement of biases only happens indirectly.
If a restaurant owner kicks you out of a restaurant, he is also expressing himself, just through association instead of speech. Additionally, he has property rights to consider. He is allowed to control the operation of his building and business. On the balance, the restaurant owner should be favored in this sort of dispute.
Why involve the cops? It's not strictly necessary. In many cases, there are private citizens that do the same job (event security, bouncers). But the cops, at the end of the day, are enforcing the the restaurant owner's rights to property and free association. The enforcement of biases only happens indirectly.