By Troy Anderson , Staff Writer Up to half of Los Angeles County's foster children were needlessly placed in a system that is often more dangerous than their own homes because of financial incentives in state and federal laws, a two-year newspaper investigation has found. The county receives nearly $30,000 per year from federal and state governments for each child placed in the system money that goes to pay the stipends of foster parents, but also wages, benefits and overhead costs for child-welfare workers and executives. For some special-needs children, the county receives up to $150,000 annually. "Called the 'perverse...