I don't think the phone will be ringing as much.” When the Hollywood actor Ron Silver endorsed George W. Bush's re-election campaign, he knew it wouldn't enhance his career.

The night after he spoke to the 2004 Republican convention we had dinner in a New York restaurant and Ron said that he expected many of his Hollywood liberal friends would cut him off. It was something he didn't relish, but he was ready for it. He thought it a price worth paying to be able to say what he thought.

And he was right to be apprehensive. Ron was - I don't think anyone who saw him would disagree - a brilliant actor. He was riveting playing Alan Dershowitz in Reversal of Fortune and Angelo Dundee in Ali. He won a Tony for his role on Broadway in Speed-the-Plow and was nominated for an Emmy for his role as the political consultant Bruno Gianelli in The West Wing. Yet after his Bush endorsement big roles were much harder to come by. His talent was such that in time they would have returned, I suppose. But, tragically, Ron died on Sunday after suffering from cancer for two years.

Apart from mourning a friend (a wonderful, life-enhancing friend), I've been thinking. What does the life of Ron Silver tell us about politics? Why should doing what he did have been so rare and so brave? And why did it have such a high price?

For most of his career Ron was an emblematic Hollywood liberal Democrat. He was president of Actors' Equity for a decade, established the Creative Coalition liberal lobby group with artists such as Susan Sarandon and Alec Baldwin, stumped the country for Bill Clinton and was a prominent campaigner for abortion rights. But after 9/11 Ron went one way, and his liberal friends another. He believed that the fight against Islamism was a fight for his liberal values and he thought that his erstwhile allies didn't take it seriously enough.

So he found himself sharing Dick Cheney's box and speaking to a stadium full of Republicans about the need to re-elect George Bush. He hadn't changed his mind on the liberal issues he had fought for all his life. He just believed that the defeat of a new form of totalitarian ideology was more important now. Ron didn't do anything as mundane as switch sides. He abandoned having a side, which is much rarer for a political figure. And much harder.

In Hollywood, supporting Bush on any grounds was completely unacceptable. In the 2000 Convention the only film “star” the Republicans could turn out was a conservative columnist who had a walk-on role as a teacher in Ferris Bueller's Day Off. (Does anyone remember him? Anyone? Anyone?) The social norm that creative types are liberals is very strong. And even those who don't share it, keep their mouths shut. Ron told me that another member of the West Wing cast (I don't think it is fair even now to say who) had confided that he agreed with Ron's position, but “he was smarter than me. He donated to the Democrats and made sure his vote for Bush stayed quiet.”

But it is not just in the movie business that there is such uniformity, is it? Such uniformity is everywhere. People adopt their political opinions largely to create an identity for themselves. Many just want to be part of a gang. If policy was all that mattered, someone who supports the liberal position on health care might be for or against a tough policy on Iranian nuclear weapons. But policy isn't all that matters - people look around at what the majority of other people like them are doing and saying, and then do it too. Dissent is hard, rebels can find it lonely.

In his book Tides of Consent, the political scientist James Stimson uses 50 years of opinion polling to trace the impact of this gang mentality.

He shows, for instance, what happened on the abortion issue in America. In the 1960s more advocates of abortion rights were Republican than Democrat, because many Democrats were Catholic while many Republicans were upper-middle-class women. However, the issue was not a prominent one and views on abortion were not correlated to party identity.

Over time this changed. Republican leaders started campaigning against abortion and gradually views on the issue began to align with party support. Professor Stimson traces a range of independent issues that become absorbed in the party debate in the same way - civil rights laws, for instance, and gun control. In other words, whatever our original view may be on an issue, we allow it to slowly dissolve into our general party identity. Pro-choice Republicans, for instance, defected or slowly conformed.

The result of this process - which is just as strong in this country, probably stronger - is a thinning of politics. Everything we know about decision-making suggests that a rich debate among people with a mixture of attitudes would be far superior to to a clash of gangs.

So to do what he did, Ron Silver needed huge strength of character. And fortunately he had it. He didn't rely for his political identity on other people's attitude to him. He loved argument, encouraged it. The last time I visited him in New York he took me to dinner and invited two of the most outspoken people in the city - the firebrand conservative writer Ann Coulter and the liberal author of Primary Colors, Joe Klein. Ron then sat back and enjoyed the inevitable huge row about Barack Obama that took place, complete with shouting and table pounding.

He simply couldn't accept or see that those people belonged in different gangs, and felt that everyone ought to know everyone else, whatever their background. (This reached a high point when he introduced me to the actor Tom Selleck, assuming that we were old friends. I knew who Selleck was, of course, having watched Magnum PI and Friends. Selleck, on the other hand, looked bemused, proving surprisingly rusty on his old directors of the Conservative Research Department of the 1990s).

And with this came Ron's courage. He would say what he believed, whoever he had to say it to. As Klein put it this week: “The list of directors and playwrights and fellow actors and political leaders he told to go screw themselves represented a who's who of the bien pensant entertainment world. ‘You don't want to ask me what happened with Nelson Mandela,' he said when he came home from filming Ali in Africa. (He didn't like the fact that Mandela embraced Yassir Arafat, who killed innocents. Apparently Jamie Foxx has the videotape. ‘It isn't pretty,' Ron admitted.)”

Wouldn't it be wonderful if there were more political activists in the world like Ron Silver? But this week I have to get used to the fact that there is one fewer.

daniel.finkelstein@thetimes.co.uk

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