Quote from nicholaf:
if the put is priced correctly (ie, fat tails, volatility smile, etc) then the price of the put is the expected payoff of the put at expiration in many scenarios. therefore, if the price of the put is indeed the expected payoff of the put, then if you do this over and over, you are not profiting from your options trades because in the end, the profit is equal to the cost. thus you are just incurring transaction costs. therefore, it is better to put all your money into the CD.
of course, if the put is not priced perfectly, then there is opportunity to profit (ie. if the imp was too high/low, the expected payoff was modelled wrong, etc).
therefore, i think we are confusing it because of the CD issue. just because the interest on the CD can pay for the premium of the put, it doesn't mean it is a good trade, because the premium of the put can be put in the cd to earn extra return.
also, it is not riskless. there is the limited risk of losing the put premium, even though you earn it back through the CD.
So this trade should just be looked upon as a pure option trade. is the put under of over priced according to your market view. when we see it as this, then it we can now see the risk involved - the premium