Robert Samuelson's column in the Washington Post does a nice job of summarizing why and how small interest groups acquire political power.
Here’s an example: A company and its workers lobby for import protection, which saves jobs and raises prices and profits. But consumers — who pay the higher prices — don’t create a counter-lobby, because it’s too much trouble and the higher prices are diluted among many individual consumers. Gains are concentrated, losses dispersed. ...
[H]e argued that the proliferation of special-interest concessions could reduce a society’s economic growth.
“An increase in the payoffs from lobbying . . . as compared with the payoffs from production, means more resources are devoted to politics and cartel activity and fewer resources are devoted to production,” he wrote. “This in turn influences [a society’s] attitudes and culture.”
The dilemma for democracies is clear. Voters expect governments to cater to their needs and wants — and one person’s special interest is another’s way of life or moral crusade. But if governments cater too aggressively to interest groups, they may undermine (or have already done so) the gains in productivity and economic growth that voters also expect.
and the telling conclusion:
Even with a jobless rate of 5.1 percent — getting close to “full employment” — the Congressional Budget Office projects a 2015 federal deficit of $426 billion. That’s one measure of overcommitment: Americans desire more government than they’re willing to pay for in taxes.