Islam, which many Americans consider a threat, has a valuable and little-noticed lesson for Western investors. Following Muslims' Shariah law, the religion's investing style avoids highly indebted companies that burn brightly -- and risk fizzling out. Amana funds, the largest U.S.-based family of Islamic-oriented mutual funds, have posted mostly so-so performances since 2009, as corporations worldwide issued a plethora of bonds to take advantage of minuscule interest rates. Unfortunately, widespread unease about Islam in the U.S. obscures the virtues of Shariah funds. Calls for preventing Muslims from entering the U.S. are just part of the trend. Seven states have barred courts from using Shariah law.