America is a representative republic. We can't all participate in public decisions, but we can choose representatives.
These legislators face a dilemma. Should they: 1) transmit the ideas of their constituents, or 2) rely on their own background? Most find a compromise, but how do they know constituents' views?
Personal contact is arbitrary. Politicians' intuitions are unreliable. Polls give a sense of opinion, but little guidance on specific legislation. The media often have an agenda, including selling advertising, and the publics' views are not constant.
Pluralism offers an elegant solution.
America is described as a country of joiners. People join together, in sports leagues, investment clubs, interest groups, et cetera.
If something matters, people seek and join others who share their views. In politics, any idea that attracts significant attention is represented by a group.
So, interest groups compete for legislators' attention, and the clash of plural views becomes a surrogate for democracy. The unseen-hand of group competition produces the highest public good.
Today, however, competition often takes the form of money and insider influence. With 13,000+ lobbyists and billions spent, has this competition become dysfunctional? Has pluralism emphasized private interest over public good, and clogged the ideas' marketplace to the point of paralysis?
What do you think? Can we rely on interest groups, especially ones we personally support? Does the market for ideas need more supervision, or should the market rule?