Infidelity is a little like flying: we feel guilty about it and the harm it does to others, but sometimes we just do it anyway. But now, serial love cheats, just like serial air travellers, can cleanse their consciences by logging on to www.cheatneutral.com, a website for "offsetting" infidelity.
Cheatneutral allows you to pay £2.50 to carry on cheating while funding "monogamy-boosting offset projects". In effect, you pay someone else to stay faithful.
As the website explains: "When you cheat on your partner you add to the heartbreak, pain and jealousy in the atmosphere. Cheat neutral offsets your cheating by funding someone else to be faithful and not cheat. This neutralises the pain and unhappy emotion and leaves you with a clear conscience."
What if you are always monogamous, or just single and celibate? You can still "get paid for not getting laid" if you register to become a Cheatneutral offset project. "All you have to do is agree to stay monogamous or single - and if we match you with a suitable cheater, you'll get paid to neutralise their cheating."
Cheatneutral is, you will have guessed, not really encouraging anyone to cheat on their partner. The website is a spoof, intended to highlight the absurdities of carbon offsetting.
As the site puts it: "Cheatneutral is a joke. Carbon offsetting is about paying for the right to carry on emitting carbon.
"The carbon offset industry sold £60m of offsets last year, and is rapidly growing. Carbon offsetting is also a joke."
Cheatneutral was thought up in a pub by Christian Hunt and Alex Randall, who work for an environmental charity in Machynlleth, Mid Wales.
"We both agreed that offsetting does nothing to cut emissions in the west," says Hunt. "So we thought of all the harmful things you could offset. We came up with Dangerneutral, where you could drive dangerously, as long as you paid someone else to drive safely."
In the end, the idea of offsetting infidelity appealed most. A US radio station showed interest, says Hunt (but "didn't get the idea that it was a joke"), and the two men had a serious proposal for a joint venture with a website encouraging extramarital affairs.
Cheatneutral has been well received in eco-circles among those who agree with the argument of the environmental writer George Monbiot that offsets "are being used as an excuse for the unsustainable growth of carbon-intensive activities".
Hunt and Randall perfectly parody the self-justifications of those who have to fly to a vital work conference or a half-term break in Spain: "Jealousy and heartbreak are a natural part of modern life. And sometimes, no matter how hard we try, it's just not possible to be faithful . . . You will be joining a global community of fidelity - a massive cheat-absorbing resource, ensuring the future well-being of millions of unfaithful couples . . . Yes, Cheatneutral is helping you, because you can't help yourself."
So far, Cheatneutral has offset 65,768 cheats and has 9,002 faithful people ready to neutralise cheaters' misdemeanours.
This suggests that the faithful currently outnumber the transgressors. Would that it were so in the world of carbon offsetting. As Hunt puts it: "My darkest fear is that cheat offsetting will become a multibillion-dollar industry but climate change will be out of control."