Fifty years ago, in August 1961, social psychologist Stanley Milgram conducted an experiment that changed our understanding of the human propensity for evil for ever. Participants were invited into his laboratory at Yale, supposedly for a study looking at the effects of punishment on memory. Asked to assume the role of the "teacher", they were then told to administer an electric shock to a "learner" every time he made a mistake. The shocks started at 15 volts but increased in 15-volt increments every time an error was made, going right up to 450 volts – enough to kill someone twice over.

In fact, the learner was an actor, and the electric shocks weren't real. The question that Milgram was really interested in was how willing people were to follow instructions. Would they stop at 150 volts (where the learner demanded to be let out, because his heart was starting to bother him), or at 300 volts (where he let out an agonised scream and then stopped answering)? How far would you go?

Milgram's colleagues suggested people would only go up to about 100 volts – certainly not far enough to cause real harm. They also thought that only about 1% would go to 450 volts, assuming that only a sadist or a psychopath would go this far. However, as every student who has recently completed a psychology A-level knows, two-thirds of Milgram's participants continued administering shocks all the way up to 450 volts.

Milgram's experiment showed us that even normal, "decent" people can engage in acts of extreme cruelty when instructed to do so by others – an idea consistent with Hannah Arendt's notion of the "banality of evil", which had derived from her observations of the trial of Adolf Eichmann – which came to a conclusion in the same month as Milgram's experiment. Arendt presented Eichmann as a bland office worker: not a monster, but a normal person more concerned with bureaucratic duty than questioning the ends to which bureaucracy is working.

The empirical contribution of Milgram's experiment is as important today as it ever was, but how relevant are the conclusions that were drawn from it? Recently historians and psychologists have started to unpick the idea that evil is banal. Research indicates that decent people participate in horrific acts not because they become passive, mindless functionaries who do not know what they are doing, but rather because they come to believe – typically under the influence of those in authority – that what they are doing is right.

David Cesarani's 2004 biography of Eichmann, for example, shows him to be no back-room pen-pusher, but an enthusiastic Nazi keen to play his part in developing creative solutions to "the Jewish problem". Yaacov Lozowick's study of Hitler's bureaucrats, likewise reveals them to be much more than small cogs in a big machine of which they had no understanding. The true horror is not that they were blind to the evil they were perpetrating, but they knew full well what they were doing, and believed it to be right.

In these terms, Milgram's studies are still relevant, not because they provide a window on to the "banality of evil", but because they provide insights into the conditions under which evil can appear banal. In particular, the key question they throw up is why participants identify with the authority rather than with the victim, and hence are willing to follow him down the destructive path he sketches out.

This same question continues to be pertinent to atrocities and abusive acts we see around us in the world today: the abuse of detainees in Abu Ghraib, genocide in Darfur, or even phone hacking in News International. In all these cases, followers have proved willing to work towards leaders not because they were blindly obeying orders but because they were working creatively towards the goals of a leadership with which they identified.

In all these cases searching for orders fails to recognise the nature of the processes involved. They involve not just passive obedience but also dynamic followership.