People said shorting Bitcoin was a no-brainer when the exchange rate was $2. When the exchange rate rocketed to $10, many serious, smart people just knew it was

People said shorting Bitcoin was a no-brainer when the exchange rate was $2. When the exchange rate rocketed to $10, many serious, smart people just knew it was a speculative bubble. Rinse and repeat for each leg up ... $32, $90, $240, $1100. Same arguments every time. Given historical volatility, I'd say fair collateral for a short sale would be 300% of the current exchange rate in USD, EUR, CHF or gold, with a margin interest rate of 6% per month.