[hombre_fatal]

This is a good example of my point.

Instead of progressing to a system resilient to the fact that you can't know how code was written, you've created a rule that, because it's unenforceable and deniable, must retreat to moralization about what someone does in private.

That might make you feel good, but it won't work.

[fwip]

The same argument applies to not including copyrighted code. I can't possibly know if a contribution is a direct copy of some private code somewhere, but it's still reasonable to have a policy against it.