like you said earlier. . .it's extremely complicated. . .but, at their heart (i.e., pure legislative intent) virtually every "tax break" is an incentive to encourage people with some extra money (or with LOTS OF EXTRA MONEY) to invest in industries and what-not that will create jobs for the masses, whether it be their own business (in the instance of sole proprietors, small partnerships and small corporations) or someone elses (in the event of widely-held, publicly-traded entities). . .no. . .i'm not kidding. however, there are a lot of really good tax attorneys and such out there, that look at the rules of those "tax breaks" for opportunities (loopholes) to legally exploit (bastardize) the inherent weaknesses in most legislation. a pure flat tax will remove most (if not all) of the incentive for investment.
like you said. . .it's complicated. . .