NEW YORK ( ETF Expert) --The city of Detroit just filed for the largest municipal bankruptcy in U.S. history. Crude oil is pushing $110 per barrel. Microsoft ( MSFT), eBay ( EBAY), Intel ( INTC) and Google ( GOOG) severely disappointed in their second-quarter earnings reports.Housing starts dropped to its slowest pace in 10 months. Also, while it may appear unlikely to market watchers, the Federal Reserve may still taper its bond purchasing program earlier than anticipated. Less money for retirees, less consumption due to the gas pump, lower sales by bellwether corporations, fewer homes being constructed and less borrowing due to elevated interest rates. Is this the stuff that stock market rallies thrive upon? Apparently so. Yet, the remarkable run-up may be running out of time. One of Warren Buffett's favorite indicators of over-the-moon stock prices is the ratio of total market capitalization to gross domestic product. According to CNBC, the net ratio stands at 118%. Previous moments in history when the ratio exceeded 100% include 1999 and 2007 -- right before humongous stock bears mauled the S&P 500 and slashed its value in half. Nevertheless, this Fed-fueled uptrend has defied analyst criticism and brushed aside guru bearishness for years. Famous doom-n-gloomers from Roubini to Rosenberg have found themselves waving the white flag. Meanwhile, perma-bulls are expecting the S&P 500 to gain at least another 10%-15% by year's end. Personally, I am playing it relatively safe with my client allocation to equities. That said, there are at least three solid reasons why irrational enthusiasm may "win out" for a while longer. 1. Underperforming institutional dollars. Hedge funds and most institutional advisers have struggled to keep pace with U.S. stocks; any effort to diversify or hedge with competing assets (e.g., commodities, currencies, foreign stocks, foreign bonds, domestic bonds, etc.) have only dragged on portfolio performance. It follows that in a "what-have-you-done-for-me-lately" investing arena, the pressure to perform has resulted in limited diversification and greater ownership of U.S. equities. 2. Political necessity. Due to the Federal Reserve's manipulation of interest rates, corporations have been able to restructure debt and buy back shares of stock; consumers have been able to purchase big ticket items like residences and automobiles.