The Founders feared factions or parties derailing their "great experiment." George Washington even famously so, called out the threat of parties (factions) in his historic Farewell Address.
Having a dual party system has forced the US into an ignorant politic characterized by framing issues in black and white, and driving people to believe the greatest sacrilege of all: a belief that compromise is the number one evil — as though it can only be one way or the other, and there is no possibility for a little of each side making a more beautiful world. America is, after all, "the Great Compromise."
The world is not a world formed in black and white. It is a world made up of the many shades of the primary colors. We cannot limit ourselves to framing and relating to a world in black and white. We must free ourselves to enjoy a world of color as reality dictates.
The dual party system makes America impotent — incapable of fulfilling righteousness. It drives ignorance and has fomented a practice of anti-intellectualism detrimental to the American psyche. It makes the US weaker. It drives intelligent people away and disenfranchises them. It favors cowardice, and those willing to partake in cowardice. It entices lying or distorting facts to make them bend to black or white. It is the cause and the driving force behind America's greatest tragedy.
Look at the number of people identifying as independent. All voices silenced in the political system we now know — and it is a situation the greatest Americans, from the beginning, feared would develop into just what it has.