Often the additional parties are the results of splits within parties and lead to the defeat of the party they left. If Buchanan had more mainstream support, he could arguably hurt Bush's presidential prospects by splitting the party. Additional parties can also play a kingmaker role in the national arena. Though the third parties may never win the presidency, they need to be included in the national debates. They play a vital role in deciding national politics and elections.
Additional parties help to define issues and other parties.
The American people should not be forefully classified into two groups. The candidates have a right to be heard. The U.S. citizens have a right to hear what they are financing. Most importantly, the U.S. people have the right to choose for themselves who they will support, this is not the job of any commission.