Sentiment on Wall Street has gotten so bad that it's good, at least according to one indicator with a high degree of accuracy. Investor optimism has continued to erode through the current correcting, with some gauges showing bearishness at multiyear highs. One in particular -- the Bank of America Merrill Lynch Sell Side Indicator -- puts sentiment "close to where it was at the market lows of March 2009," the firm's strategists said in a report Monday. That date will be familiar to many investors as it marked the Great Recession low and preceded a 200 percent bull market surge....