When writing options, you must be hedged. Otherwise you will eventually blow up.
I love it when people have a 1-line answer for a 21-page thread. This is absolutely correct. This thread really should end right after Daniel's post.
I am not sure how many times I have brought up 1987 on this site, but many. Please don't tell me that it won't happen again. I hope it won't, but believe it's best to live as though it could.
Here is an example of how selling naked puts might work in a scenario like 1987. Today, I can sell the SPY 15 Apr 200-strike put for about $455. I think my margin will be about $1500 (depends on rules of broker). If SPY is down 22% on the day of expiration, I think I would need to pay about $4500 to $5000 to repurchase the put, but I can only guess at this because I don't know what the volatility would be like. However, another likely scenario is that before I can make the repurchase, 100 shares of SPY could be put to me for $20,000.
So, there are 2 ways I can deal with this problem (I like #2):
1. I can keep $20,000 in cash. Eventually I'll need it, but most of the time it will lie around doing nothing. No, I can't just blow out that account and start another. The broker can come after me for what I owe. As you can see, it would be easier to just write covered calls, which amount to the same thing as keeping all that cash around. Covered calls at least have the virtue of allowing me to know my maximum loss.
2. Buy the insurance. For example, today I can buy the SPY 15 Apr 175 put for about $41. On the spread, my margin is about $2000 and my maximum loss is about $2000. Or if I want to, I can buy a longer-term long put that I can sell many shorter-term puts against. Yes, I am overpaying for the insurance. But this is still a great return on my money: about 20% if the puts expire worthless.
Just make sure you are bullish on the underlying and have a method for figuring out when you should no longer be bullish on it. For example, I personally would not be doing this on SPY right now.