It is doubtful that Bono will be too concerned about the latest controversy surrounding him. Embarking on a tour of South Africa with U2, the rock revolutionary told an interviewer that he supported the singing of "Kill the Boer", an African National Congress anthem. It was an incendiary thing to say: last year, the song was banned as "hate speech" by the South African High Court after the ANC's youth league leader, Julius Malema, had taken to singing it at rallies. White lobby groups have argued, with some justification, that it was inciting the murder of white farmers.

The timing of Bono's remarks was tactless, and his grandstanding of his liberal opinions from the safety of privilege unattractive, but the awkward fact is that he is almost entirely right. Comparing "Kill the Boer" to the kind of IRA rebel songs which he and his family used to sing when he was young, he told the interviewer, "This was the struggle of some people that sang it over time." He then added a qualifier: "It's where and when you sing those songs. There's a rule for that kind of music."

The idea that songs from the past, unacceptable as their lyrics may be, contain lessons for today is an important one, although I suspect that Bono would be reluctant to follow it to its logical conclusion. Popular music provides an intimate unofficial history of the times in which it was written, revealing what is really happening in people's minds and hearts. More often than not, those things are, by the standards of later generations, unrespectable, embarrassing or downright scandalous.

The problem lies in defining what Bono calls "that kind of music". He may personally have a warm liberal feeling for what are now called "struggle songs" but if the anthem in question were not "Kill the Boers" but "Kill the Jews", "Kill the Homosexuals" or "Kill the Irish Rock Stars", he might have been rather less robust in his defence of it.

I am currently researching a musical show and a Radio 4 programme about trouble-making music, and it's clear that it's a divisive subject. Songs are a powerful, potentially dangerous medium. There are those – including, shamefully, some academics – who genuinely believe that the race songs of the first part of the 20th century are so repugnant that it would be better if they were quietly forgotten. They point to the fact that the ugly descendants of that music, profoundly nasty right-wing country songs, are still being recorded and posted on the internet.

Gender is even trickier. Our culture is interestingly relaxed about masochistic songs sung by female singers – "a kiss with a fist is better than none," sings Florence and the Machine – but anyone appearing in public singing the old vaudeville number "The Dumber They Are, the Better I Like 'Em" or, that old hit from the 1940s "Catch 'Em Young, Treat 'Em Rough, Never Tell 'Em Nothing" is likely to get a rough ride from audiences.

Reactions to songs of the past invariably reflect anxieties of the moment, and are invariably subjective. Bono may feel nostalgic for Irish rebel songs of the past, but I remember feeling distinctly queasy when hearing a senior BBC journalist bellowing one of those songs at a party during the 1980s. An IRA hit-list had recently been discovered and my father's name was on it.

The South African whites who argue that "Kill the Boer" is music at its most dangerous are right when it is sung at a political meeting, but wrong to try to censor it out of existence. Increasingly, there is indeed a rule for "that kind of music". It is that any song from the past which reminds contemporary audiences of the bigotry, violence and cruelty of the human spirit is better suppressed in the name of decency and a quiet life.

In fact, we need to listen to those songs, not ignore them. Sometimes the dumber they are, the more we can learn from them.

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