In a democratic society, when a political interest group exceeds a certain size, the diverse and sometimes conflicting economic interests that can be found in almost any large group of people tend to surface  Once these conflicting interests have surfaced, they can make it impossible for the political interest group to unite behind a common program
Yet to have the political impact necessary to influence legislation, a group must be united
A political interest group can become ineffective by expanding to include as wide a membership as possible.