You could even make the argument, that by not increasing production over the last few years, they have helped the US build a substantial increase in our oil production. Our real growth would not have happened in the low prices of early 2009 had continued.
in a free market price would be stable
Actually, commodities markets show pretty clearly stable prices are not normal outside of a cartel willing to manipulate price. I'm not arguing OPEC is a good thing. But utopia doesn't exist in the oil industry with or without OPEC.