Law enforcement authorities don't know why suspected gunman Wade Michael Page burst into a Sikh temple in Oak Creek, Wis., on Sunday and opened fire, killing six before he was shot dead by the police.But many American Sikhs say they do know this: Their community has been targeted by a growing number of hate crimes since the 9/11 terrorist attacks. The New York-based Sikh Coalition reports more than 700 such incidents since 2001. The question is: Why?