Racial discrimination in housing and employment is illegal.
Discrimination laws are unconstitutional. No surprise there.
The fourth amendment requires a search warrant be served before a LEO can enter a person's house, property or business. Why? Because the government can't be trusted to always do the right thing. Even though they are in a sense employees of the people, they can't be trusted. In other words, a business owner doesn't have to open his doors to any government agent, unless they have a properly signed warrant. Yet discrimination laws force business owners to open their doors to total strangers.
Free Association. Free association is the right to associate with whomever a person chooses so long as they don't initiate force. That means if a person doesn't want to associate with you they can refuse you access to their property.
Depends on the business.