In fact it is the fringe parties that introduce many ideas, and serve as checks to such complete amorality. There are several policies and ideas in both the Republican and Democrat parties that originated in third parties or fringe parties. "Fringe" parties are "fringe" for a reason. They're not devoid of some good ideas, but, being "fringe", they can't steer the mainstream.
But they do steer the mainstream! The near complete absence of fringe parties in black politics -- it's all Democrat, a black Republican is considered fringe -- attests to the streering that occurs in white politics on account of the fringe.