But in truth it is a competing alt-coin that uses the bitcoin infrastructure. Its like you said you are going "sailing" but are actually just sitting in your car on a ferry. MC is technically a service on top of Bitcoin but in essence it is a separate coin.
Bitcoin is more like an aircraft carrier named
Honeybadger which was built for the masses which is in an ocean, owned by no country, and surrounded by sharks. And Mastercoin is like a small
motocross track with 100 or so individuals trying to organize where to put in its first jump.
The original honeybadger video if you missed it.