As the United States, the world's greatest melting pot, struggles with the racial thorn in its criminal justice system, one sobering truth should not escape ethnically diverse nations. Racial divides left untended can prove intractable, despite decades of other social improvements. US President Barack Obama's assessment strikes a grim note: "This is something that's deeply rooted in our society, deeply rooted in our history."

It is certainly something that no society can afford to ignore when the security that all citizens expect from the police and upholders of criminal justice - including the security that law enforcers themselves are entitled to - is called into question by reciprocal fears born of prejudice.

In the US, the racial profiling of suspects by white policemen is often done unconsciously. Stronger police action is directed against black males, in particular, as they are seen to be associated with criminality and aggression. Did such perceptions of a menacing threat prompt the police officer at the centre of the Ferguson riots to say he felt "like a five-year-old holding onto Hulk Hogan", before he killed the 18-year-old black suspect? Standing at 1.93m and weighing 95kg, the policeman was hardly a toddler against a suspect who was no taller than him, although heavier.

Resentful minorities, frequently subjected to stop-and-frisk routines on the street, in turn view the police as a threat, leading to fight or flight responses. What adds to the downward spiral is a community perception of bias among local prosecutors, as was the case when the Ferguson shooting was brought to court.

Some studies in the US indicate that a mere 37 per cent of blacks have confidence in the police, whereas 59 per cent of whites have faith in cops. The divergence will become harder to reconcile as long as systemic issues are not tackled firmly and more cases occupy the public gaze like that of Rodney King (over 23 years ago) and Michael Brown (this year). President Obama's creation of a Task Force on 21st Century Policing rightly places the focus on building public trust by, for example, reviewing the growing militarisation of municipal police forces.

Together with the National Security Agency's mass surveillance and the Central Intelligence Agency's brutal torture programme, the excessive violence of American law enforcers harms the superpower's global image. It undercuts the moral high ground adopted by the US in serving as a progressive influence in the advancement of the rule of law and international justice. A model for the world in many other respects, America owes it to itself to root out poisonous social attitudes and troubling flaws in its criminal justice system.