ONE PUZZLE about Rand Paul’s much-discussed interview with MSNBC’s Rachel Maddow last week is why ever he allowed himself to get drawn into a discussion of his doubts about the Civil Rights Act of 1964. One day after winning the Republican Senate primary in Kentucky, was that really a topic he thought it would be useful to explore on national television?

I suspect that’s exactly what he thought. I imagine that in the flush of his victory, he thought the moment was right for a fearless demonstration of libertarian principle — for making it clear that when it comes to liberty and the Constitution, he makes no exceptions. Not even for a law as iconic as the Civil Rights Act.

All he ended up demonstrating, however, was his inability to thoughtfully defend his position. Which was a shame, because the principle Paul was contending for — that freedom necessarily includes the freedom to make unpopular, even wicked, personal choices — is not frivolous. Regardless of your view of the Civil Rights Act, that is an argument worth hearing. But Paul failed to make it.

Maddow asked Paul: “Do you think that a private business has the right to say we don’t serve black people?’’ This was his reply:

“I’m not in favor of any discrimination of any form. I would never belong to any club that excluded anybody for race . . .. But I think what’s important about this debate is not written into any specific ‘gotcha’ on this, but asking the question: What about freedom of speech? Should we limit speech from people we find abhorrent? Should we limit racists from speaking? I don’t want to be associated with those people, but I also don’t want to limit their speech in any way. . . We tolerate boorish and uncivilized behavior because one of the things freedom requires is that we allow people to be boorish and uncivilized.’’

Paul went on to explain that he embraced the 90 percent of the Civil Rights Act that targeted “governmental racism or discrimination,’’ such as the Southern Jim Crow laws and segregated schools. It was only the remaining 10 percent, the ban on discrimination by private businesses, that he balked at. Personally, he would shun any Woolworth’s lunch counter that refused to serve blacks, but he didn’t think government had the right to force Woolworth’s to desegregate.

The weakness in that position is that it was government that forced Woolworth’s and other establishments to exclude blacks in the first place. Jim Crow was imposed by the state, often through police power and over the objection of local businesses, and backed by courts that refused to enforce the 14th Amendment. The Civil Rights Act rightly aimed to uproot not just public discrimination, but private discrimination that government malice had entrenched.

But that was nearly a half-century ago. What is the justification for laws banning private discrimination today, when Jim Crow is dead, racism is overwhelmingly abominated, and a black man is president of the United States? If a bigoted store owner today wants to refuse service to blacks, why should he be barred by law from doing so?

“Unless it’s illegal,’’ Maddow told Paul, “there’s nothing . . . to stop the country from re-segregating like we were before the Civil Rights Act of 1964.’’

Does anyone really believe that? With or without a federal law, segregated restaurants would be as unthinkable today as “No Irish Need Apply’’ signs. A firm that adopted a “No Blacks’’ policy would set off a storm of public outrage; if it didn’t back down, it would be driven out of business within a week.

But the larger point is that behavior must not be criminalized merely because it is ugly. The same Constitution that guarantees our individual right to express odious ideas should likewise entitle us as individuals to engage in odious discrimination. So long as there is no violence or fraud, we are far better off deciding for ourselves whom we will and won’t associate with.

That can be a hard truth to swallow, as Supreme Court Justice Oliver Wendell Holmes Jr. observed long ago. “If there is any principle of the Constitution that more imperatively calls for attachment than any other it is the principle of free thought,’’ he wrote in 1928. “Not free thought for those who agree with us, but freedom for the thought that we hate.’’

Jeff Jacoby can be reached at jacoby@globe.com.

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