Another issue is that mastercoin is centrally controlled by one party, all issued by one public key they call the "exodus address".
MasterCoin is not centrally controlled. This is simply a misunderstanding of how MSC works.
Mastercoin was built on top of Bitcoin because DaCoinMinster saw how alt coins are victim of ideological exclusion in the community and how Bitcoiners are inflexible fanatics. It's going to be a good learning for them.
We all know that Bitcoin needs small transactions to move off-chain if we don't want shit to hit the fan in the near future when adoption rate takes off. But instead of that Mastercoin brings more in-chain bloat at a whole new scale.
Mastercoin's success will be Bitcoin's Nemesis."
This was from the Ripple forum. They are a little sore that bitcoin people don't like Ripple. The bias against alt coins IS part of the reason I chose to build on top of bitcoin. I also share that bias

Bitcoin should be able to scale as needed to handle a high volume of MSC transactions in the near term. If bitcoin can't scale in the long term, we'll have to migrate to another block chain. (yeah, it's possible)