Superintelligence - A critique of Nick Bostroms arguments

Why is everyone afraid of artificial intelligence? I'm more afraid of natural human stupidity (which is already infinite according to Einstein!).  Superintelligence would just balance that out ;-)But seriously I think Nick Bostrom has some flawed arguments in his talk:1. He assumes that the work which is necessary to create a higher and higher intelligent being is linear (or even sublinear) with the IQ. But maybe this is not the case.