The point of HN is to discuss 'Anything that good hackers would find interesting.' This isn't the same as being smart. I don't think it's a good idea to use that language as the basis for trying to influence someone, as it's easily interpreted as an underhanded suggestion that others are not as smart as you, and it implies that smartness is the major relevant scale with only one notable axis; omitting knowledge and experience, for example.
Nor does it seem useful to equate "smart" to "serious" or a lack of "offhandedness". Shows like QI, the puns in scientific journals (eg, in Angewandte Chemie at http://pipeline.corante.com/archives/2009/10/13/those_zanies...), the IgNobel awards, and the humor of David E. H. Jones in his Daedalus columns, etc. strongly suggest that your observation of a strong anti-correlation between those traits is more a personal belief.
Which major catastrophe? Doomsayers love to say "catastrophe" and then not say what they mean.
Are you talking about Chernobyl, the catastrophe where they literally had to disable every single safety in the system? Yes, if you disable every safety and intentionally ignore your engineers, the next two thousand years are going to have a bad time in that area.
But if you're saying that in the general case people are unable to build safe systems that harness nuclear power, that seems empirically mistaken.
(It would be better to assume every question on HN is a serious one. The point of HN is to be smart, and smart people rarely resort to offhandedness to make their points.)