Let's see.
@TheBigShort s main argument is that most of the insurance contracts underwrite highly idiosyncratic events, such as fires, deaths or car accidents. The sheer diversity of their pools mitigates their risks and they can further mitigate it by laying it off to reinsurer companies (who, in turn, have even more diversified books). On this other hand, a stock option is a combination of the company risk with the market risk. Market risk is systemic in it's nature and it's impossible to diversify away. In fact, one can argue that company-specific risks are efficiently priced while the market risk is rich by nature (e.g. that's why dispersion works).
My argument is that insurance price is dictated by a cartel of providers and that naturally creates pricing that's favorable to them. An options market has steady two-sided professional flow so by and large it's going to be efficiently priced. Of course, there are some pockets of inefficiencies, there are forms of risk aversion specific to various players and, finally, there are regulatory pressures, but all of these are secondary to the market flows.
Last but not least is mark to market. An insurance provider is not required to post more capital as the risk of his positions increases. In fact, their standard approach is to keep no more than the regulatory reserves and invest the balance into all sorts of risky assets. An option seller has to be comfortable with the MtM fluctuations, even if the actual event is extremely unlikely.