A two-party system is not necessarily worse than a multy-party system. They both have their flaws. Just as one example, party programs in multi-party systems such as in Germany are not worth the paper they are written on, because after the election the parties will go into negotiations and come up with an entirely different program. With two parties, at least you know what you vote for.

This is a great lecture on the topic with much more depth to it:

www.youtube.com/watch?v=T3-VlQu3iRM