It's complete oversimplification, but the reasoning behind trickle-down Reagonomics is that when you reward a successful manufacturer (for example) with favorable tax structures, they will expand their businesses and create even more good, high-paying factory jobs. Many would benefit.
If you gave these same tax credits (in the form of $100 bills) to the wino down the alley, he would purchase booze, fur coats, prostitutes, and a couple of fancy cars. Before long, he would be penniless and sleeping in the gutter again. Nobody would benefit.
The point is that American businesses have exhibited leadership and we as a society wish to encourage this leadership so that it will help a large number of people. It isn't "cruel" that we're providing incentives to brilliant citizens who will likely provide opportunities to hundreds, if not thousands, of other Americans.
Sincerely,
~ Blue Jays ~