One night last week, the No 26 was packed.

At this hour, the top deck would normally have been awash with spilled lager and fruity language, as barflies and party-animals started to make their way home from Edinburgh. For once, though, it was quiet. The passengers were middle-aged and well dressed. Instead of vinegar and chips, an air of self-satisfaction wafted down the aisle, emanating from those of us who had just been partaking of the festival's delights.

But had a filthy tramp come up the steps and passed his cap among us, would we have fished out coins more willingly than those who'd spent the night in front of Celebrity Masterchef, or would we have put our heads down and reread our concert notes, reminding ourselves how much the tickets cost?

It's an interesting question. At this time of year, when the biggest arts jamboree in the world is in full swing, one needs to be steely - or skint - not to be tempted by something, be it a busker or comedian, a symphony or play, or a talk by a bestselling author. One also feels guilty if one does not partake, because no matter what the show, whether it's held in the Usher Hall or a minibus, there's a common belief that the arts are good for us in more ways than one. We are supposed not only to be entertained, but to emerge enlightened, refreshed, more thoughtful and considerate.

How then to explain that Hitler, who wanted to be an artist, revered Wagner's work, and owned a full set of Shakespeare? Or that Stalin loved ballet and opera, and Saddam Hussein wrote novels?

Thankfully, the taste of a few megalomaniacs does not undermine a general principle, namely that the arts play a refining role in the lives of individuals and society. Even the morally depraved are capable of being touched by art, however shallow or short-term its effect. Otherwise, what value has it if it can only preach to the converted?

But that is where I have difficulty with the comforting, often smug idea that the arts actively improve us. On a personal level, a play or a book can indubitably change the way we think. Indeed, psychologist Steven Pinker makes a strong link between reading fiction and greater compassion.

But can a symphony, or a jazz trio, or a ballet have the same effect? Sure, they can make one happier, which in turn inspires generosity and tolerance, but an afternoon digging the herbaceous border might have the same effect. None of these activities, though, would render anyone less homophobic or racist or misogynist if that was the way they were inclined.

I would suggest, instead, that as an ethical force for good, the arts make their most important impact on society as a whole. Not only do they inject fresh ideas into the country's veins, but they offer a platform for a level of public dissent or controversy that those in power must tolerate if not condone, lest they be accused of philistinism. From the very beginning, the arts have acted as guardians and spokesmen for those whose voice is weak or silent. Yet much art is consolatory rather than challenging, aesthetically enriching rather than morally uplifting. It is not the stuff of social revolution, but of an afternoon's untaxing leisure.

And what's wrong with that? Beauty, solace or exquisite harmony are an essential part of human life. Not everybody, however, can partake of it fully. And that's where the problem lies. The correlation between education and appreciation of the arts is unavoidable. Money is part of that equation, but so too is a greater understanding of art forms and their meaning. It's no surprise, then, that art goers are also more likely to be politically engaged and financially better off. The ethical benefit the arts is meant to exert is thus hard to disentangle from sensibilities that were already sophisticated or open to change.

All one can say with assurance is the arts are a civilising force in the widest sense. None of us is completely human without them, be it soap opera or the Ring Cycle. They might not make us saints, but they cannot do us anything but good. If I were a beggar I'd sit outside the Festival Theatre or the Underbelly, and pray that I'm right.