Why do women like cads?

"About 60 percent of the women said they would prefer to have sex with a cad when considering a brief affair," said Daniel Kruger, a social psychologist at the U-M Institute for Social Research (ISR), the world's largest academic social science survey and research organization.

...the findings imply that the dad versus cad distinction is intuitive to women and remains a key element of contemporary mating strategies. Women's preference for cads for short-term relationships supports what evolutionary psychologists call the "sexy son hypothesis," Kruger said. Even though cads aren't good bets to stick around and help raise children, the genes that make men successful cads will be passed along to their sons, who will increase their mothers' eventual reproductive success by providing numerous grandchildren.

That being said, few women want their daughter to marry a cad:

...the distinction between dads and cads is intuitive enough that women showed a strong preference for dads [the contrasting male category, defined as caring, nurturing types] as potential sons-in-law. Only 13 percent of the women said they would prefer to see an imagined 25-year-old daughter engaged to a cad. "A cad would be less likely to provide paternal support for offspring," Kruger said, "which means that a daughter might turn to the maternal family for help. That could adversely impact the grandmother's overall reproductive success."

Here is Kruger's home page. Here is a link to the journal Human Nature, which lists the article as forthcoming. Here is the home page of co-author Maryanne Fisher.

My take: I can't get my hands on the original paper. But the explanation, as offered, leaves a gap. It shows that a "cads equilibrium" is stable, once in place. But why are the sons of cads, themselves cads presumably, seen as sexy? One woman may want a cad, if she knows that other women will (later) want her son. But where does the female preference for cads, viewed more generally, come from?