Clearing negative balances will just encour Clearing negative balances will just encourage people to gamble/leverage up in the future knowing they will get a 'bailout' if things go wrong. Ideally these firms should make punters pay something even if it is only 10% of what is owed to discourage this in the future. Now if they are promising you will always cancel negative balances every time then thats a different thing. Then people are free to leverage up all they want.
Suggest you read the agreement. This from Oanda Asia Pacific. See item 15. http://www.oanda.sg/documents/pdf/fxtrade_legal_agreement.pdf
There is always a key lesson when an extreme event like this happens. While leverage is one of those things you have to manage carefully, I don't think that was the key lesson here as this big move would have spanked you regardless of the degree of leverage you had on. So what do I think the key lesson was this time? Know what you're trading. That means don't just take setups based on charts, indicators, and a false sense of loss protection from stops. The CHF was a pegged currency and that made it susceptible to the whims of the SNB. There is no moving average, Fib ratio, or oscillator that would have told you this. You had to understand what it was behind the chart.