Interesting, thanks for the link. I've never run into that before. I've downloaded a lot of software, much of it open source. I've only downloaded from the Mac App Store maybe twice ever. But this is the first time I've gotten completely denied. Is it because it was a zip file with an executable inside, rather than an installer? Or as someone else mentioned, because it isn't signed at all? Are all the open source projects paying for signing certs for their OSX installer packages?
Again, thanks for the link. That's probably the only time I'll run into that, it clearly isn't my usual use case, but I'm glad you could back up the assertion with something I could see for myself.
I do agree that it should be clearer how you can run the executable if you really do trust it.