An extremist Christian might gain comfort from the idea that life is a gift from God, but then use the same idea to justify the murder of a medical doctor performing abortions. An extremist Muslim might find acceptance and brotherhood in submission to the will of Allah, but then strap a bomb to his or her body, in the belief that it is pleasing to God.
Putting aside the implications of possible psychological pathologies, the difficulty in such cases arises from the lack of an obvious point of reference against which to judge the benefits and harms associated with particular ideas, and what they are used to justify.
As the lives of religious martyrs and secular heroes demonstrate, seemingly obvious criteria such as physical harm and loss of life are often inadequate. These are times thought to serve the greater good, however this be defined.
In the case of religious ideas this difficulty is compounded by the horizon of possible benefits and harms extending beyond the empirical concerns of this life, and this world.
Modern secular democracies have attempted to circumvent this difficulty by organising themselves in accordance with the Enlightenment idea of the separation of church and state.
Enlightenment thinkers such as Voltaire, Kant and Hume argued that the 'light of reason' should replace the authority of the Bible, and that a willingness to think for ourselves should supplant a passive acceptance of tradition.
The price paid for the religious tolerance that spread throughout Europe in the post-Enlightenment period was the confinement of religious ideas to the private sphere of faith and conscience, while the public sphere of politics, economics and education was to be guided by ideas that could be rationally justified or substantiated on empirical grounds.
The secular heirs to the Enlightenment’s emphasis on the rational control of the public sphere may have the benefit of an intellectual ethic that requires all claims to be rationally tested, but the 'this worldly' focus of these claims is restrictive in its own way.
In seeking to organise the public sphere in accordance with ideas that can be justified empirically, modern secular societies have relied upon a broadly utilitarian approach to seeking the "greatest good for the greatest number".
Exactly how this should be understood and calculated remains a matter of debate, however the underlying aspiration is that the best interests of individuals and communities should be understood in terms