Suppose for example that http://gnome-look.org/ offered packages in some format where it was trivial to verify that installing the package wouldn't write any files into system script directories such as /etc/profile.d . (It is not easy -- perhaps not even possible -- to verify such things about .deb packages. Perhaps if they were Nix packages http://nixos.org/nix/ instead then it would be easy.)
Suppose then that the administrators of http://gnome-look.org/ ran a script which confirmed that the eye-candy packages didn't install anything other than the appropriate eye-candy plugin code. (Note that they don't need to inspect any source code themselves -- they just have a script which inspects each new package when it is uploaded to confirm that nothing gets written outside of the appropriate location for eye-candy plugins.)
Now here is my point: nobody needs to make judgments about the moral character of the authors of the plugins! This hypothetical Principle-Of-Least-Authority package management system (of which Nix may be an example or at least an ancestor), plus this hypothetical script that the owners of http://gnome-look.org/ execute automatically on all new uploads, plus this hypothetical Principle-of-Least-Authority eye-candy plugin mechanism (of which Google Native Client is an example), combine so that you can happily invite the author of this malware to go ahead and submit a whole bunch more eye-candy plugins to http://gnome-look.org/ , and millions of users can safely download his latest creations and stare at the pretty pictures.
So the point that I'm trying to emphasize here is that discerning between good guys and bad guys among the authors of the software that you rely on is *not* the only way to defend against malware.
And a good thing too, because that strategy is utterly hopeless for a large-scale software ecosystem. It is an appropriate strategy for Dunbar's-number-scaled ecosystems in which you basically know everyone involved personally and can form coherent opinions about each person's character. In other words, it was probably a great strategy for our ancestors ten thousand years ago, and that's probably why we continue to think of it as the right and natural thing to do today, even though it is utterly useless for today's situation.