Opposition is going out of fashion. It's hardly surprising, given the nature of the attacks on London, that the Commons appeared united in its exchanges on the subject. Yet even the prime minister looked taken aback by the effusiveness of Michael Howard's remarks about him earlier this week. The Tory leader was not merely polite, he gushed. There was no "however", no silky sarcasm; it was surprisingly straightforward praise. Tory calls for inquiries, derisively dismissed by Hazel Blears, had virtually evaporated. Across the Commons there was the nearest to complete unity I can remember.

Now we know that those responsible were homegrown suicide bombers, there will be a more political and anguished debate about what exactly drove them to their evil acts, but there are few signs that the new mood of unity, at least in mainstream politics, is shifting.

Few dare break it. George Galloway, the Respect MP, got an icy bucketload of disdain for saying Tony Blair had "paid the price" for Iraq. Charles Kennedy, choosing his words with great caution, said that Bush and Blair "can hardly be surprised" when members of the public drew the same link between Iraq and the war on terror that they had drawn. He was quick to say the terrorists alone were responsible for the bombings but even that didn't prevent him being heavily biffed by No 10 for naivete. Making any connection between the government's policy on Iraq and terror attacks in Britain, at all, is apparently beyond the pale, in some strange way it is seen as disrespectful to those who died.

Certainly this is no time for cheap political points. Anyone who tried that would be rightly condemned. But we should be alarmed at the worried, finicky nature of political debate about these matters, the lack of democratic robustness. Callers to radio phone-ins and letter-writers to newspapers seem to have no such qualms.

This political timidity is all the more pertinent because Howard's lauding of Blair was a fashionable act in the modern Tory party. With the prime minister again on a political high, Conservative modernisers the Notting Hill mob are now advocating a more consensual attitude to politics. George Osborne, the 34-year-old shadow chancellor, kicked this off in a speech last week: "By disagreeing with the prime minister when he attempts to do the right thing, we undermine our credibility when we criticise him for doing the wrong thing."

Was this a bit of careful positioning to help David Cameron, the likely main challenger to David Davis for the leadership? Though Davis was also notably calm and impressive in the aftermath of the attacks, and is consistent in his general attitudes, his enemies in the party are going after him for being too inclined to bite any Labour ankle whatever the issue, simply too nastily aggressive. If the Osborne comments were meant to be part of a Cameron campaign, Cameron himself immediately supplied supporting evidence, saying at the weekend that when Blair had "done Conservative things ... in the long-term interests of the country" then "you should support it".

The two Tory modernisers were referring to policies like foundation hospitals and tuition fees - both highly controversial among the general public. Yet when the two main parties agree, what hope is there that a different point of view will be heard? Nobody wants merely stupid yah-boo politics, of course, and a lot of the time we get too much of that. The Tories in the Howard era were indeed inclined to zig-zag, looking for a headline or a soundbite; the Labour charge of opportunism during the election hit home, a bit, because it was true. But the Commons is in real danger of sliding into a sentimental, soupy consensus, too scared of being accused of saying anything that gives comfort to the many-headed and anonymous enemy.

If Britain is supposed to be engaged in a struggle to defend British values, then we should recall what the most important ones actually are. They are not stoicism, good humour, even courage; but genuine democratic liveliness and a commitment to free speech. Without dissent, freely expressed, and the vigorous testing of arguments, the Commons has no purpose, other than formal rubber-stamp for the executive. And if ever we needed that testing, we need it now.

The "war against terror" is unlike any previous war, and may not be winnable in traditional terms. As the Leeds connection shows, it is genuinely a war without borders. One purported reason behind the Iraq invasion, like the Afghan war, was to take and control territory otherwise used as a terrorist base. But as the US marines bloodily discovered in southern Afghanistan this month, it is a hard task. Far from "draining the swamp", the Iraq war multiplied the territory available to Islamist extremists.

Then there is Islam itself. Events in the Middle East have given new excuses to an extreme Islamist doctrine that is as evil as any variant of religious fascism can be. Yes, most Muslims are hostile to the bombers and the radicals, but there is virulent anti-semitism and anti-western rhetoric that has to be confronted and opposed.

Saying that the bombings have nothing at all to do with Islam is fatuous - as fatuous as saying that there is no connection between Christians and anti-abortion militants in the US. It might be a perverted strain of Islam, or one variant of Christianity, but there's a connecting "of". This too needs to be honestly and openly debated in parliament, without the nervous thin syrup of evasion.

Here is what will happen if politicians evade their duty to talk and argue. First, as we have seen, the media steps in to usurp the role of the Commons, in far more virulent and one-sided ways. MPs bang on all the time about how broadcasters and editors are stealing their authority, but it is mostly their fault. They have to shrug off predictable newspaper attacks on them for saying unpopular things, and they have to keep going, responsibly and using careful language. The public will listen. Columnists are already debating the bombings, and the war before that, with a directness MPs shrink from. Is this the right way around?

Some kind of deal needs to be struck. Newspapers need to stop having hypocritical hissy-fits every time an MP says something outside the consensus. MPs then need to stop being so timid. We don't elect them to be vicars or social workers.

If this doesn't happen, not only will governments continue to make mistakes unchecked by argument in parliament, but people will continue to turn away from democracy itself. Already, around the school gate, in the coffee shop and in the pub, talk about the war on Iraq, about radical Islamists, is angry.

Parliament is where these things need to be expressed because if not there, then it will be in the media and eventually on the streets. If the polite, uncontroversial exchanges after the bombings were a respectful lull then, yes, we should welcome that. If they are the beginning of a new mealy-mouthed, mumbling kind of politics, then we should protest. Mutual respect for genuinely held differences - that's essential. But this is the very worst time for smothering political debate.

Speak up, speak out

In the wake of the bombs, we don't need soupy consensus in parliament but a vigorous testing of arguments