"What is the moral worth of an ideology that is willing to make every possible legal argument they can think of to defend discrimination by private enterprise?"
President Eden made the moral case against the government banning private discrimination; I will make a slightly more practical one. There are lots of things in the world that are bad or immoral (however you want to define that): cocaine addiction, prostitution, adultery, misogynistic films and music, alcoholism, racism, not giving money to charity, and so on. We can clearly see in many of these cases (like laws against drug possession and prostitution) that using the force of law to stamp out these things has been, on the whole, a net negative. The harms from outlawing these things have been or would be worse than the harms that they create. It's easy to believe that the harms resulting from outlawing private discrimination could be worse than the discrimination itself. It probably wasn't in the 1960s, but it probably would be now.
""But they also opposed the laws codifying segregation. "
Prove it."
I provided an example, remember? Plessy v Ferguson? The railway companies opposed the law because of the expense, and they supported Homer Plessy's case.
The larger point you're missing is that, historically, the most important forms of racial oppression have resulted from the oppressive actions of the government or from the misapplication of the proper role of government. Slavery in the USA simply could not have existed without both state and federal legal protection. Segregation existed because state and federal governments introduced laws codifying it. It's only been in the last forty years or so that you can even meaningfully separate the harms of racism and racial oppression from the abuse of government authority. The problem has been government, so you should understand why people don't find it convincing that making the government even stronger is the best answer.
"You acknowledge that libertarians oppose the 'expansion of federal power' even and especially when that power aims to protect excluded classes of people from the tyranny of their state governments."
Not entirely true. Banning private discrimination is a separate thing. I think almost any libertarian would favor federal action that struck down racially discriminatory state laws, however. For example, I can't think of any significant libertarian objections to the 1965 Voting Rights Act off the top of my head. Currently, the Libertarian Party is opposed to state drug laws, which have an obvious racial element. I imagine there would be more of a split among libertarians on the recent state immigration laws like in Arizona and Alabama, but I think a solid majority of libertarians oppose them.
Also, again, Goldwater personally favored civil rights, and as a city council member, he supported local civil rights ordinances. But he didn't want the federal government involved, and he was extremely suspicious of using government power to promote social goals. If you don't understand that difference, I'm not sure how much simpler I can make it.
As an aside, you're much overstating the impact of communism on social change in the USA.