`Playing God' is a cliched, but effective, piece of rhetorical
claptrap intended to inflame feelings against certain groups of people in positions of power: in practice,
scientists and
doctors. It is effective as
framing because it implies, without explicitly stating, a series of unjust
stereotypes about these professions, and also because it makes an appeal to people's sense of religious propriety. Strangely enough, even in societies where relatively few people believe in the
Old Testament God who appears in the phrase, it is still a mainstay of
soapbox oratory. It neatly combines accusations of arrogance,
hubris, irresponsibility, callousness, blasphemy and irreverence; a phrase tailor-made for the use of the
Grand Inquisitors protecting humankind's morals against the dangers of
innovation.
It is claptrap, however, because the people who are routinely accused of 'playing God' do not deserve the slanderous implications of the phrase, whilst others who show greater arrogance, irresponsibility and callousness in the use of power are ignored or excused.
The activities of God usually thought of in connection with this phrase are deliberately creating forms of animal and human life (Genesis) and arbitrarily consigning individual humans to their fates (Old Testament, passim). Genetic engineering is thus a target, although conventional animal breeding, which had already created, for example, dogs unable to breathe properly, is apparently not a problem. In vitro fertilization was also stigmatized as `playing God'; and as we see in the first writeup here, so is the midwife or doctor who decides to ends a life which could only be one of torment or oblivion. But somehow, this accusation is never made against those who consign others to the death penalty or indefinite imprisonment without trial -- however unjust and arbitrary these fates may be in individual cases.
Of course, there are many other things God got up to: perhaps most conspicuously, genocide or mass slaughter of people who happened to be on the wrong side. Or more beguilingly, some neat tricks like turning a stick into a snake and back again. Strangely, no-one accuses military commanders or dictators, illusionists, or charismatic faith healers of `playing God' -- even though the consequences of abuse of military power, or exploitation by charlatans, can be dire.
Deliberate inconsistency in application is only one aspect of this phrase's deviousness. The other is the connotations of playing. So doctors and scientists are painted as enjoying the exercise of power, as frivolous and irresponsible in using it, and therefore overweening and callous. I should not have to point out that these are unjustified accusations with no more basis in fact than racial or sexual sterotypes. (It's true that some professions do see more than their share of delusional, power-drunk behaviour -- for example, head of state, or the leader of a religious cult.)
But while Fagin and Uncle Tom have thankfully faded from public discourse, the fictive images of the medical student Frankenstein and the `mad scientist', created by the scientific illiterates Mary Shelley and Nathaniel Hawthorne among others, are alive and well and influencing opinion. (See for example Nathaniel Hawthorne: Science unrestrained.) Of course there are real examples of scientists and doctors who do misuse power or take actions without considering their moral implications. This does not justify smearing the whole of a scientific or medical endeavour with the failings of a minority of practitioners.
Perhaps the group of people who may most accurately be said to be 'playing God' are the theocrats: those who seek to determine the fates of thousands or millions of others -- in the belief that they themselves are God's representatives on Earth.