From Beethoven through to John Lennon and from Stiff Little Fingers through to Pussy Riot, music is filled with political commentary. What is much rarer is musicians not just espousing radical opinions, but signing up to an established political party. And it's something they do at their peril - even just for the reason that politicians aren't exactly top of the pops when it comes to cool.
For many people, music and politics just don't mix. Is there anything more cringeworthy than seeing a middle-aged politician trying to get down with the kids - or anything more likely to raise hackles and cries of hypocrisy than a rich pop star telling us how great socialism is?
Musicians more often than not end up disillusioned with their experience - remember, for example, Noel Gallagher looking back in anger on his drinks at 10 Downing Street celebrating the election of Tony Blair at the height of the 'Cool Britannia' era? Sinead O'Connor is the latest singer to take the jump and join a party, in this case Sinn Fein. It probably came as a surprise to some, but O'Connor's career has been littered with bizarre twists, including becoming a priest.
It was also notable that she lent her support somewhat conditionally. On the one hand she said she wanted to join the party because she would like to see a "socialist Ireland", while on the other she said she would like to see the current Sinn Fein leadership step down.
Some wits said that at least this meant that at last there was one Sinn Fein member who wasn't toeing the party line and backing Gerry Adams.
Other views weren't so generous. The contradictions inherent in a rich pop musician - however genuine their beliefs - espousing socialist ideas were immediately pointed out by some. One comment on the Belfast Telegraph website said: "A millionaire pop star that lives off the royalties of labours performed in the past with a reward system designed and set up by capitalists joins a left-wing socialist party which believes in redistribution of wealth to people who refuse to work. Well, where do you start..."
Another said: "This will be another of Sinead's short-lived escapades. As the saying goes, 'she couldn't finish a fish supper'. A self-publicising narcissist..."
These were just two of dozens of comments. Opinion was polarised, some for and some against - and even more left bemused.
Of course, this is the danger when a musician ventures into the political arena. You only have to look at the particular kind of vitriol that's reserved for Bob Geldof and Bono, which reared its head again recently with the release of a new recording of Do They Know It's Christmas? As Stuart Bailie, of the Oh Yeah Centre, wrote in this paper a few weeks ago: "These days, you will struggle to find a positive word about the pair of them."
John Lennon was never shy of expressing political opinions - though he never joined a political party. The former Beatle and agitpop practitioner was murdered in 1980 by Mark Chapman, who thought he was a "phoney", a man that he believed professed to hold radical views but in reality had sold out and was living in luxury at the Dakota building near Central Park in New York.
Lennon had faced criticism for years as a figurehead for the anti-Vietnam War movement. He was well aware of these criticisms and told Time Out in 1972: "I certainly don't agree with the philosophy that you can't be left wing because you're rich. I just happen to be rich by a rather dubious process called showbusiness." Unfortunately, his often eloquent defences of his opinions didn't stop some from seeing him as a hate figure.
In Britain, the most famous - or infamous - case of musicians backing a political party was the Red Wedge movement in the mid-1980s which backed Neil Kinnock's Labour Party. The Eighties were a decade when the divisive policies of Margaret Thatcher led to some prominent musicians aligning themselves to the opposition.
Of course, Red Wedge failed in its attempt to get Labour elected in 1987 and the movement fizzled out afterwards. Today it is probably no more than a footnote in musical history - though its concerts would be fondly remembered by many who attended them.
The most famous members of Red Wedge were Billy Bragg and Paul Weller. Some would argue that Weller's involvement with the Wedge was the kiss of death to his career at the time with The Style Council. He faced criticism, sometimes from fellow musicians. Peter Hook of New Order told Melody Maker in January 1986: "I've seen all this socialism bulls**t that Paul Weller goes on about… I mean Paul Weller is a really big business… and he's got the power just with what he does to affect a lot of people's lives."
It was only when Weller returned without the overt politics in the early 1990s and embarked on a solo career that his success returned. Later Weller said: "All the politicians I met on the Red Wedge tour, the Derek Hattons and the Cuddly Kens, they were just celebrity figures out for themselves. I'm just not interested in anything political any more." A more successful link-up has been Bruce Springsteen's backing of Barack Obama - but America's first black President has always had a showbiz quality about him anyway.
Even for Springsteen, however, the risk was always that he could alienate right wing fans, many of whom thought Born In The USA was a straightforward paean to his home country rather than a nuanced take on the Vietnam War.
For political parties, the risks of signing up celebrity members are that they can never really be fully under their control. They are famous in their own right and by their nature are difficult to control.
Sinn Fein didn't exactly sound overjoyed by its newest member's statement on Facebook.
A spokeswoman defended the current leadership. She said: "The membership of the party selects the Sinn Fein leadership every year at our ard fheis.
"As a member, Sinead O'Connor would have an equal say in that process."
O'Connor will also find that her ideals may not rhyme exactly with Sinn Fein's agenda - and it's unlikely she will be reticent about criticising policies.
This is the woman, after all, who ripped up a picture of John Paul II live on American TV.
It seems that for now anyway O'Connor thinks, to paraphrase her most famous hit, that nothing compares to Sinn Fein.
Already she's talking about a revolution… but whether anyone in Sinn Fein is listening is another matter.