I've not regretted reading some of his books, but I strongly advise anyone who wants to maintain some respect for him to avoid his Twitter feed at all costs. And I'm one of those highly analytical types that isn't overly burdened by emotional sensitivity. The man really is just that grating in real time. I get the impression that in his books he does some rewriting to limit his more egregious impulses.
While assuming normality will very often lead you to underestimate risk, fat tails can easily cause you to over estimate your risk.
Or think about the case of "robust" regression in which errors in a linear model are assumed to be from a fat tailed distribution like Student's T. This means that your model is not suprised by outliers. The consequence of this is that your model assumes that mode data is near the center and ignores extreme observations.
As a philosophical device fat tails are very helpful and interesting, but as a practical tool for modeling they are far from a panacea