IT'S easy to see why film stars, ego-driven as many of them are, might feel that it's not enough to captivate the world for a couple of hours at a time – one must also change it, irrevocably, in a way that doesn't fade as the memory of a movie does.

Both Sean Penn, right, and Angelina Jolie have recently been mocked for their attempts to do this, the subtext being that instead of fooling around in foreign politics, they should just stick to acting.

Jolie, the mother of six children, long-term UN Goodwill Ambassador and one half of the global golden couple known as Brangelina, has directed a moderately controversial film about the rape of women during the Bosnian conflict. Sean Penn, meanwhile, waded into a brewing row over the impending 30th anniversary of the Falklands war, by lending his support to Argentinian claims to sovereignty of those islands, and accusing Britain of being "colonialist, ludicrous and archaic".

Penn is neither a politician nor a diplomat, so when he opened his mouth, the world listened. They listened to what he had to say about Argentinian claims to sovereignty of the Falkland Islands, or the Malvinas as he called them. They listened to him postulate that Prince William's deployment to the Falkland Islands was "unthinkable". And then they ridiculed him. Or at least, some did. The adventurer Ben Fogle, a close friend of Prince William's, tweeted that he should be fed to crocodiles. Falkland war veteran Simon Weston branded him an "idiot and a fool". And many others just wrote him off as an ignorant star, before moving on to criticise his movies and general personality. This response says everything about our relationship to celebrities. We look to them to prick our interest in world events, then declare they are only stupid stars.

Meanwhile, Angelina Jolie's film In The Land of Blood And Honey, had its premiere in Bosnia, amid stories that she has received death threats, and a sense that friction is building in a region where the conflict remains fresh in the memory. There is nothing especially wrong with Jolie making this film. Many a director has chosen a difficult story from a country that is not their own. But looking at the reviews, the story's validity is apparently being questioned because Jolie is its creator. In some people's eyes, her attachment to the project makes it seem more questionable.

When we, as a society, crave the words of a particular group of people then treat them as entirely lacking in credibility, there is something awry. Penn may be famous, but, far from lending legitimacy to the Argentinian claim over the Falklands, his comments have – in the UK at least – caused those claims to be mocked and treated with contempt.

It's easy to belittle grand statements by celebrities as ill-researched. But the truth is, in these instances, both Penn and Jolie know something about the situations they comment on. While Jolie may not have experienced the Bosnian conflict, or be particularly close to those who did, she has researched it for her film, spent time with those who experienced the war all those 20 years ago. And if, as some have pointed out, she is not neutral on the subject, why should that be an issue? A movie is not a thesis. Jolie has confessed her film is one-sided: most movies, most stories, are.

Meanwhile, many have suggested that Penn is so lacking in knowledge that he is unaware the inhabitants of the Falklands are choosing British governance. I see no evidence of this. Rather, it seems to me that Penn has an alternative view that disregards the rights of those islanders and prioritises instead the issue of the global distribution of resources in a debate that increasingly revolves around the oil discovered in the area. David Cameron was right to say that, in a sovereignty debate, the UN would back the islanders since it is "part of the UN charter to support self-determination", but that doesn't mean Penn's view has no moral validity.

The problem is not whether these stars are wrong or right – you can make your own mind up on that. Rather, it's the media power they wield, and the possibility that their statements might be triggers to real, possibly violent events. Among other things, Penn has accused Britain of colonialist attitudes. But he should stop and look at his own behaviour. Both he and Jolie are vehicles of a kind of cultural imperialism. They may champion good causes, but ultimately they come to them as larger-than-life, famous Americans. And at the heart of their projects, for all their attempts at virtue, is a rather arrogant, almost colonialist belief in the idea that the big, famous guy can step in and sort out the muddle that the stupid little people have got themselves in.

Recently Penn appeared on television expressing pride in the work he had done in relief in Haiti. He said his experience there had helped him get over his divorce from Robin Wright. The problem is, we can't see these celebrity posturings as anything other than a desperate bid to salve their own consciences. One can't, for instance, help wondering whether Angelina Jolie made In The Land of Blood And Honey to make herself feel better about the fact she made such Hollywood spy nonsense as Mr And Mrs Smith. This shouldn't matter if the cause is just. But somehow it does.

We can't blame the celebrities. They are just performing a role we increasingly require of them. Every charity, every cause, every politician, is always looking for some star to stand by them. It's depressing to see leaders of South American states clamour to pose next to a Hollywood star whose words are just taken as a joke over here. Especially as we know all over the world, all too many politicians and organisations are doing it.

Meanwhile, we, the global public, are the ones to blame, since we seem to have an inability to find interest in anything that doesn't have a star's name or face attached.

l Film review: page 62