What role should "special interests" play in political campaigns?

Here is but one perspective:

"One man’s evil 'special-interest group' is another’s advocacy organization as pure as the snows of the High Sierra.

The Sierra Club is no less a 'special-interest group' than the U.S. Chamber of Commerce. Both pursue political agendas. Both get considerable media attention. The members of both give money to political campaigns to influence lawmakers.
The subjectively defined 'special-interest group' is at the heart of debates over campaign financing. U.S. Rep. Tom Cole, R-Moore, wants to abolish public financing for presidential campaigns. State Rep. Richard Morrissette, D-Oklahoma City, wants to create a system of 'voter-owned' elections."