''Because lust is there to essentially lead us to pursue people into bed, which is a very current goal, it tends to focus our minds on the present and on detail,'' he says.

''People in a lustful state are more detailed (in their thinking), focused on the trees rather than the forest'', which leads to ''decomposition of a problem into smaller pieces'', according to Dr Laham. Even a relatively tepid form of lust, such as is induced by looking at nude pictures or certain words, causes people in experiments to perform better on analytic reasoning problems that involve working through details step by step, such as , ''If A is bigger than B, and B is bigger than C, is A bigger than C?'', Laham explains.

His book The Joy of Sin musters evidence from psychology experiments by researchers around the world to argue that the seven deadly sins (lust, gluttony, greed, sloth, wrath, envy and pride) are not necessarily bad. ''Under certain circumstances these things can bring about a range of benefits, including making one happier, smarter, more creative and increasing pro-social behaviour,'' he says.

People feeling proud of themselves will stick at a task longer and achieve greater success.

People with time on their hands (evidently slothful, in this busy era) are more sensitive to the needs of others and more likely to help.

With his mission of challenging the notion that the seven deadly sins are ''uniformly bad'', Dr Laham did not feel the need to amplify the obvious point that the sins can be bad for you as well.

Most people already have a sense of that, he believes. Research also shows, for example, that high lust levels can trigger risk-taking sexual behaviours and sexual aggression.

He is spruiking his case from the podium at the Sydney Opera House's Festival of Dangerous Ideas next weekend. That in itself, depending on your point of view, might lend support to the competing talk by Bishop Julian Porteous of the Catholic Archdiocese of Sydney. He says it's time to look again at the devil as a real being who is active among us, because modern psychology is an inadequate explanation for evil.

Dr Laham's argument that the seven deadly sins can be good for you ''certainly would be quite contrary to the Christian belief'', says Bishop Porteous. As for the thought that ''we are all sexual perverts'', the subject of Irish author Jesse Bering's talk, ''I don't know what he is going to argue but I would probably take a different position'', Bishop Porteous laughs.