I think there are three kinds of people who believe we should repeal parts of the civil rights act and allow businesses to discriminate based on race, religion, sexual orientation, etc. You've got:
A. Libertarians who believe that if we give businesses the right to discriminate, that's not only what our founding fathers would want but also everything will work itself out anyway because of free market or supply and demand or freedoms and liberty something.
B. Racist/sexist/otherwise bigoted people who own a business or wouldn't want to serve black/female/gay people if they did own a business.
C. People who have no understanding of history or how horrible and racist and bigoted some people are.
You can't argue with A, because they either understand what they're advocating for and don't care or they don't understand what they're advocating and cannot be told. The ghost of Christmas future would have to visit them and show them what would happen if the civil rights act were repealed for them to understand that anti-discrimination laws are a large part of what is preventing black Americans (among others) from be treated as lesser people and suffering greatly in large portions of the country.
You can't argue with B, because they want an America where black people are treated as sub-human. Or gay people, or Jewish people, or in rare cases, everybody except themselves.
You can argue with C, because their opinion is usually not well formed enough to make them immune to developing a cohesive point of view on the subject. It is to this group that I remind them that my ancestor died because of discrimination. The only reputable hospital he could get to for an emergency appendectomy refused to treat him because he was a Jew. He went to the only hospital that would treat Jews and they "accidentally" killed him. I put that in quotations because they killed a lot of people they were trying to save. Just business as usual.
So many people are mistaken about the effects of discrimination. Multiple posts have referred to the effects of discrimination as being merely "offensive," implying that the only reason we have these laws are so that minorities won't be upset about not being served. No, discrimination would literally destroy lives. So believe whatever you want, but remember that when you argue that we should do away with anti-discrimination laws, you're advocating for a system under which people are allowed to die when they would be saved if they were white, or christian, or straight. Is that a system you'd call just?