Generally ideas are thought to be dangerous when they threaten an entrenched authority. Galileo was sued not because he claimed that the earth revolved around the sun — a "hypothesis" his chief prosecutor, Cardinal Bellarmine, apparently was quite willing to entertain in private — but because the Church could not afford a fact it claimed to know be reversed by another epistemology, in this case by the scientific method. Similar conflicts arose when Darwin's view of how humans first appeared on the planet challenged religious accounts of creation, or when Mendelian genetics applied to the growth of hardier strains of wheat challenged Leninist doctrine as interpreted by Lysenko.
One of the most dangerous ideas at large in the current culture is that the "free market" is the ultimate arbiter of political decisions, and that there is an "invisible hand" that will direct us to the most desirable future provided the free market is allowed to actualize itself. This mystical faith is based on some reasonable empirical foundations, but when embraced as a final solution to the ills of humankind, it risks destroying both the material resources, and the cultural achievements that our species has so painstakingly developed.
So the dangerous idea on which our culture is based is that the political economy has a silver bullet — the free market — that must take precedence over any other value, and thereby lead to peace and prosperity. It is dangerous because like all silver bullets it is an intellectual and political scam that might benefit some, but ultimately requires the majority to pay for the destruction it causes.
My dangerous idea is dangerous only to those who support the hegemony of the market. It consists in pointing out that the imperial free market wears no clothes — it does not exist in the first place, and what passes for it is dangerous to the future well being of our species. Scientist need to turn their attention to what the complex system that is human life, will require in the future.
Beginnings like the Calvert-Henderson Quality of Life Indicators, which focus on such central requirements as health, education, infrastructure, environment, human rights, and public safety, need to become part of our social and political agenda. And when their findings come into conflict with the agenda of the prophets of the free market, the conflict should be examined — who is it that benefits from the erosion of the quality of life?