In the endless babbling torrent of news, it's easy to miss the small signs of how a culture – and a country – changes. For me, a marker almost as sweet as a black man in the White House is currently flickering across Ireland's cinema screens.

Clint Eastwood is the quintessential icon of the old US: an icy everyman who made his fame cursing liberals, shooting down suspects and slaying bad guys on screen. But now, in his eighth decade, Eastwood has done something remarkable. He has been making beautiful, understated movies that apologise for the filth he pumped out early in his career – and propagandise for a very different America. Yes: Dirty Harry has turned pinko-peacenik.

Eastwood caught the tail-end of the uncomplicated Us vs Them cowboy flicks of the '50s, where Indians were evil, scalping savages who had to be destroyed by the white heroes. The films were gorgeous, romantic accounts of a genocide, told adoringly from the perspec­tive of the genocidaires.

But Eastwood found his most iconic role as a new kind of urban cowboy. The 1971 film Dirty Harry was the first of the wave of backlash movies explicitly taking on the '60s counter-culture and accusing it of destroying the US. Harry is an old-style cop, fond of torturing confes­sions out of suspects. His colleagues boast that he "is an equal opportunities hater – spics, niggers, kikes, dagoes – especially spics".

He sets out to catch a killer but at every turn he is emasculated by insane liberal regulations. The new laws prevent him breaking into homes without a warrant, committing tor­ture or harassing suspects. Appalled, Harry spits: "That man has rights? The law is crazy!" Pauline Kael, the greatest film critic of her time (or any time) famously called the film "fascist".

But then something odd happened. The old black-and-white world of Dirty Harry bled away – and a subtle filmmaker emerged. There were hints of a change in Unforgiven, his 1992 western, where an old gunslinger was traumatised by the violence he had inflicted in his earlier life.

Since then, Eastwood's films have been populated with people broken by the kind of casual violence inflicted by Dirty Harry. The Changeling is the true story of what happens when the police disobey the rules to achieve their goals. Flags of Our Fathers is the true story of the soldiers who raised the US flag on Iwo Jima during the second world war – and how the Native American soldier there, Ira Hayes, returned to face internal apartheid and abuse. The companion film, Letters From Iwo Jima, is even more bold, told as it is from the side of the Japanese soldiers. Eastwood was attacked by the likes of Rush Limbaugh for becoming "liberal".

With his latest film, Gran Torino, Eastwood makes his repentance explicit. He plays Walt, a cussed old Korean war veteran living alone in a neighbourhood increasingly populated by immigrants. Walt could be Harry in retirement, cursing the "babbling gooks" who move in next door, clinging to his guns.

It becomes clear Walt is broken by the violence he committed decades earlier. "You want to know what it's like to kill a man? It's goddam awful and the only thing worse is being given a medal of honour for killing a guy who just wants to live."

The film shows how far Eastwood has come, echoing Dirty Harry in a smiling form of apology. Where Dirty Harry sacrificed the law with violence to attack liberals, Eastwood's Walt uses the law and non-violence to defend immigrants.

In an age of forced apologies, here is a real one. This shift in one of its greatest icons is – I think – a helpful, hopeful sign of the wider shift in American culture. Although it was obscured by the backlash of 9/11 and the Bush years, the US has slowly become a more liberal and open-minded society. Look at the difference between the reaction to the My Lai massacre in Vietnam and the Abu Ghraib horror in Iraq. When My Lai broke – the deliberate massacre of a whole village, including children – 40% of Americans defended it, and songs celebrating it topped the charts. When Abu Ghraib broke, more than 90% were repulsed.

The Dirty Harry racism and brutality is abating, as the country's civil rights movements slowly win. That doesn't mean the government will follow Walt and public opinion. They are often driven by forces that aren't as accountable to democratic pressure, like corporate power – but in time, they too can be eroded. If Harry Callahan can say sorry and change, anyone can.

Go ahead, America – make our day.