Corrupting public debate?
There's a clear assumption in Andrew Norton's question that there was once a time when public debate was uncorrupted. Perhaps I missed it.
Public debate is corrupted whenever people are denied the information they need to form opinions from which they can operate within the society in which they live. It's true that the Howard Government limits access to information, the release of which does not endanger the state but may prove embarrassing politically. It's not true that they are the only government that has done, is doing or will do this.
Marr's analysis should have covered this, but in focusing on Howard it falls down on two levels. First, it's pointless to stand up for for investigative journalism when journalists are so content to be spoon-fed. Second, it depends on what you mean by "dissent".
A journalist who wanted to investigate education policy (for example) would get some press releases from the relevant minister, some press releases from the opposition, cobble together a few hundred words and job done. The fact that the story would bear no relevance to those who work in education would be irrelevant to the average journalist. The journalist who spent time and effort visiting local schools and speaking to teachers and parents would get a story that might testify to the effectiveness of government policy, and the connection between official policy and objective reality. This would prompt a paranoid flurry from the State Education Department's media unit and possibly the minister's office, to which management would not necessarily stand up for the journalist. "Investigative journalism" today means checking the fax machine to see if another press release has been received so that it can be cannibalised and turned into a "story".
In The Age, Frank Moorhouse wrote that the press should be "constantly alert to the vulnerability of freedom of speech, not only when it is threatened by the state but also when the quality of freedom of speech is damaged by intellectual laziness, intellectual intimidation, easy certainties, and all the fashionable sensitivities and peer pressures that creep into our social communication". He was referring to literary magazines, but the same might also be said of news outlets.
In terms of dissent, the rights of a small group comprising both thugs and latte-sippers chanting "whaddawewant whendawewannit" does not constitute "dissent". Demos might have been scary in 1789, they might have had an impact in 1917, and they were somewhat notable in 1968, but they contribute nothing in 2007. For the most part they are irrelevant, and if it's Howard v protesters then Howard will win every time.
What constitutes dissent today? This is an important question if you're concerned about silencing dissent, or if you're trying to develop policies for a post-Howard Australia. Marr should have devoted more thought to that, as it's becoming clear that you can only defeat John Howard by outflanking him - by changing the debate so profoundly that he can't credibly participate in it.