I personally think that it's a rather bad idea to start with a closed source. Many people will want to have a look at the sources before compiling and running the daemon/GUI.
You can't really prevent people from creating forks, they could hack the binary after all. I'm sure MC2/Netcoin's success wouldn't be affected by clones, and I think the devs shouldn't worry about it. It will happen one way or another, but what makes a cryptocurrency successful is the trust people put in it, and I think releasing the sources at launch will lead to more trust.
But that's just my opinion, of course.