“The pursuit of an infidelity is a biological drive. We underestimate our ability to withstand temptation.” So says Noel Biderman, the founder of site dedicated to enabling extramarital affairs. Big Wall Street firms tend to avoid brands like these, but Ashley Madison is doing so well that some firms are finding it hard to withstand the temptation to put their money behind the site. From Newsweek’s Lynnley Browning: Wall Street Loves a Cheater.