Democratic politicians and liberal groups, including unions, often rail against corporate tax loopholes as unjustified raids on the public treasury – as they should. Loopholes are particularly troublesome during periods, such as this one, when state and local budgets are leaking red ink and basic public services are being slashed. But one multimillion-dollar loophole draws vocal support from those who usually oppose corporate tax breaks – one that happens to benefit a heavily unionized industry whose top executives are overwhelmingly Democrats and contribute lavishly to the party's candidates and causes. That would be Southern California's movie and television production community....