Why do we need alternatives to Bitcoin? I don't understand why people need to create alternatives to Bitcoin such as litecoin. Why were these created? What's the point? You can't answer those questions using the same arguments for why Bitcoin was created.
In addition to Lohoris's answer, the reason that litecoin was created was to be as resistant to custom built hardware just for mining the coins, it uses scrypt as its cryptographic function. Scrypt was specifically designed to make it as expensive as possible to create hardware that is specifically good at doing that hash function. I personally like this because I do not like the idea of buying hardware that can only do SHA-256 to mine cryptocoins.

There is also ppcoin (pdf warning) which is aimed at not relying on constantly using electricity to keep the network secure. In this way it is very distinct from bitcoin.