This is definitely a horrifying story, and I feel terrible that you had to go through this! That being said, I'm not sure that open source software is what's to blame here; it sounds more like Sourceforge (along with the nasty people who stole your project, of course) was the main issue; I think the lesson that I and others can learn from is not that open source allows theft, but that relying on a single external service (Github, Sourceforge, etc.) for everything can lead to a loss of control.