For sure, but the return distribution of equities at least was historically highly negatively skewed. There can be upside volatility in stocks, but it has eithe

For sure, but the return distribution of equities at least was historically highly negatively skewed. There can be upside volatility in stocks, but it has either no persistence or it happens just after a massive crash. Taking this skewness into account, it is not unreasonable to consider short puts more risky in a very handwavy and back-of-an-envelope calculation. Of course, other assets with more symmetric distributions (FX?) might have no such bias.