Yes, it is dangerous. It was also dangerous to invest in energy at the beginning of 2008, 2007, 2006, etc.because energy had already enjoyed a nice run. While commodity prices are looking more and more like a bubble, no one knows how long the bubble may last or how big it may be. Those who waited, thinking commodity prices were topping out, have been wrong all year.
There is a good chance that much of the gain of the YTD or last year could disappear very quickly if we get signs of lower oil consumption due to a recession, etc. But it that occurs, the market for equities will likely be bottoming and you'll see other asset classes start to climb. That's what diversification is all about--- putting disparate asset classes together in the hope of smoothing out an otherwise very bumpy ride.
Scott