Not sure why sites like Blockchain.info displays Firstbits representation of addresses so prominently...
The argument against firstbits is "it encourages block chain spam". But that is like saying that people are not going to throw trash around parks, because trashing the environment is bad. People are actually using firstbits, and will continue to do so, because using firstbits makes their own lifes easier. They don't care about the block chain. Tragedy of the commons.
Most of people don't throw trash around parks. Last time I looked there was much more trash in the trash cans than scattered around the park. The argument against firstbits is rather sensible.