Radicalism and fundamentalism are, etymologically, base concepts.

They are to do with roots and foundations. It is, therefore, quite natural that those in the mainstream of opinion should use the terms, rather lazily, as a condemnation, while those to whom the label is applied become the more convinced that their views are not low, but basic.

Describing any thought or doctrine – Islam, Christianity, socialism or anything else – as radical, whether that is meant as approval or abuse, has, of course, nothing to do with the truth or value of the belief itself. Any belief powerful enough to attract support is almost bound to be radical.

But what all ideologies recognise is that certainty of one's own righteousness is dangerous. The example Christians will recognise is the Bible's condemnation of the Pharisees, but the same sentiment is present in the Koran, which (in "The Cow") condemns those who create disorder, but present themselves as righteous. The sanctimony which Burns skewered so accurately in "Holy Willie's Prayer" isn't confined to any one religion; nor, for that matter, is there any group of believers exempt from it.

The poem, however, looks at that kind of self-deception satirically. Burns saw hypocritical religious fundamentalism as something worthy of scorn or mockery, rather than something which generated terror, and – luckily for us – since his time, that has been the prevailing attitude of liberal Western democracies. For most of human history, and most of the world, however, it has not been the norm.

Since the Enlightenment (as that self-satisfied term suggests), people in the West have, for the most part, had the luxury of thinking themselves above hunting down heresies, or conducting witch-hunts. It has been an illusion created by secularism. The fact that most Westerners see fundamentalist religion not just as reprehensible, but incomprehensible, hasn't conjured away oppression or violence. All that happened – as the history of the last century shows only too clearly – is that the ideologies used to justify aggression were given political, rather than religious, labels.

The attacks on Muslims which have been reported by the organisation Faith Matters since the appalling murder of Drummer Lee Rigby are founded on the same sort of evil as his killing. Just as Drummer Rigby seems to have been attacked solely because he wore the uniform of a British soldier, so mosques and individuals have been assaulted purely because of what they represent.

The actions of anti-Islamic extremists spring from a failure to recognise that it was individuals who were responsible for the enormity in Woolwich, not the religion which they espoused. Similarly wicked acts have been perpetrated by adherents of all sorts of other ideology; violent criminals have never been short of ways to justify their own murderous behaviour.

It is heartening that there has been unequivocal condemnation of Drummer Rigby's murder from the majority of Muslim leaders. By contrast, the YouGov poll finding that 63% of the population believes that the majority of Muslims are good British citizens may be up 1% on last year, but it still seems to me to be a worryingly low figure.

It is even more alarming, and entirely illogical, that two-thirds of people believe there is bound to be a "clash of civilisations" between British Muslims and white Britons. Any potential clash has nothing to do with the ethnic background of those concerned – and anyone who thinks it does, whether they call themselves British Nationalists or Islamists, is by straightforward definition motivated by nothing but racism.

The more difficult question, which has been the most urgent global crisis since the atrocities of 9/11, is whether there is an inevitable clash between Islam and Western civilisation. Such a clash is, of course, inevitable if Islam is defined by the criteria of Islamists. But to do so would be like defining all of Christianity by the criteria of Westboro Baptist Church in the United States, which pickets synagogues and protests against homosexuality. Mainstream Baptists and other Christians have no difficulty in identifying it as a hate group, just as the vast majority of British Muslims have no trouble seeing Al Qa'eda as terrorist murderers who are not remotely representative of their religion.

What is more, if one compares the history of Islamic civilisations with nominally Christian countries, it is hard to conclude that it is a uniquely dangerous religion. Very few people would think that Spain under the Moors, for example, was a more oppressive or bloodthirsty regime than England during the religious turbulence of the Tudor period.

Anyone who values liberty must regard it as vital to resist terrorist attacks and to challenge attempts to create oppression. But most British Muslims do not aim to impose sharia and Taliban-style government on the rest of us any more than most Christians want to frame legislation based on the teachings of fundamentalists from the Bible Belt of the United States.

Many religious people hold beliefs which seem out of step with contemporary secular societies and, indeed, one of the definitions of liberal democracy is that they must be free to do so. But very few believe that they have a right violently to impose them on others.

Many of us believe that it would be better if society adjusted itself to the priorities of religion, though the majority opinion (shown, for example, by the Kirk's recent divisions over gay clergy, or by critics of the Catholic Church's views on contraception) is probably that religious teaching should move with the times.

In either case, though, it is not difficult to distinguish between the teachings of any of the world's major religions and the behaviour of regimes which professed to be acting in their name.

The West's current unease about Islamic radicalism is obviously justified by the real attacks conducted in its name. What cannot be justified is to claim that the problem is intrinsic to any religious or ethnic group. The menace of violent and murderous behaviour lies in the behaviour, not in the justification advanced for it. Thinking that those who murder in the name of Islam represent most Muslims is like claiming that Timothy McVeigh, who was responsible for the Oklahoma bombings, represented anyone who approves of the Constitution of the United States (the justification he gave for his own terrorist atrocity).

We can all disagree on ideas and ideologies, but if we wish to continue to be free to do so, we should not confuse what people believe, or the group they belong to, with how they behave. We can recognise criminal behaviour when we see it; but it's just criminality that needs policing, not thought.