There are several disadvantages of a two-party system including the regimented party values politicians must follow, the inability to compromise, thus the inability to make effective change and the extreme polarization of parties. The two-party system also keeps independents and moderates from being able to act on any worthwhile ideas they share that do not fall squarely within one party.
The primary problem with the two-party system is that it has created polarized parties that are only interested in their own agendas. When a moderate comment is made, the party will criticize the politician for the comment and take away support. This forces many politicians to follow their chosen party's guidelines and beliefs wholeheartedly without any room for flexibility or independent thought.
An example of the party problem can be seen with the comments Senator John McCain made when running for U.S. president. He was asked what he would do if his daughter were to want an abortion and he stated that he would not interfere with her decision. He said he felt that it was her decision as to what she wanted to do with her own body. This comment, though it did not endorse abortion, was not fully in the anti-abortion belief system so the Republican Party criticized McCain relentlessly. These critiques happen in both parties and force candidates to take extreme party sides and beliefs. Then when the other party wins, they spend their entire time in office working to undo everything that the other party has done. This makes it difficult for lasting, beneficial progress to be made on a political scale.