Over the next two months the constant beating of drums and the open parading of sectarian hatred will dispel any lingering conscientious doubts in the nationalist ghettos concerning the IRA's bombing of Manchester.

Those who organise and defend the prolonged Orange folk-fest of strut and swagger will blithely overlook the important contribution they are making to ensuring the IRA's immunity from suffering the full moral consequences of Manchester, of the Shankill bombing, of their brutal "punishment" beatings of petty criminals, and of their torture and summary execution of alleged informers.

There is no justice until there is justice for all. The hypocrisy of Sinn Fein only survives by virtue of the hypocrisy of many of those in the "British and unionist camps who condemn them.

After a relatively short time, the enormity of the Manchester attack will live on only in the minds of the victims and the local residents who narrowly escaped or were close to it. Just as Manchester succeeded Canary Wharf, as the Greysteel atrocity succeeded the Shankill atrocity, as a hundred other moral outrages were succeeded by later and different ones, the story will move on.

The politics of the latest atrocity "continues to apply, and from time to time directly influences immediate government and public policy as indeed should happen, within careful and measured parameters.

But those who would urge the total isolation of Sinn Fein in present circumstances should consider carefully what cause they are serving. Would such action reduce the pool of tolerance in the nationalist communities for republican militancy, or would it widen it? Would it reinforce IRA hardliners in their resolve, or would it discourage them from further outrages?

The argument for the total marginalisation of republicans can only be based on a conclusion that they are uniformly irredentist, closed to all rational debate and devoid of moral scruples.

To act upon such a conclusion - tempting though it may be in the aftermath of recent events - would be to lump upwards of 100,000 Sinn Fein voters into this fundamentalist category. If would surely encourage more of them towards a sufferance of violence than the opposite.

The elimination or eclipse of the IRA demands a more sophisticated approach, including an understanding of where they come from and what drives them.

Certainly, there are old-style fanatical and fundamentalist elements at the influential core of republicanism; people whose single-minded aim would be to bomb and shoot their way to a united Ireland regardless of ethical considerations.

They could not survive, organise and thrive, however, without the support of many thousands of others whose ideological commitment is by no means as rigid.

That wider stratum of republican support is certainly generated by the pragmatic experience of long-term oppression, discrimination and the denial of justice, particularly in regard to key emotive events involving life and death.

Because of the continuity of political and sectarian tension over 25 years and more, the unremitting presence of the trappings of militarism, an armed police force and sweeping emergency laws, Northern Ireland is unlike Britain or the Republic.

The finer political detail of how devastating bombs in Dublin influenced the passage of tough anti-subversion legislation in the Dail in the early 1970s has largely disappeared from public consciousness in the Republic because "normal" life resumed primacy.

In Britain, it is safe to say, the public conscience is not afflicted by pangs of guilt over the hundreds of deaths in the sinking of the Belgrano or other dubious aspects of the Falklands war. Again, these were passing interruptions to the "normal" flow of social life.

Not so in the North. The killing of 14 civil rights marchers by the Parachute Regiment in Derry on Bloody Sunday, and the subsequent "cover up", are as central to nationalist consciousness today as they were 24 years ago.

The dehumanisation of republican hunger-strikers, the systematic ill-treatment of prisoners in Castlereagh Holding Centre, the litany of controversial security-forces killings - all of these and more are persistent, prominent and influential factors in nationalist perceptions.

The legacy of unresolved injustices and the fears of renewed sectarian pogroms - revived regularly by intimidating Orange parades - have encouraged an ambivalent attitude to IRA violence.

There is an inherent dishonesty and lack of elaboration, also, in regard to the repeated warnings of a possible resumption of loyalist paramilitary violence. The minority population is all too aware that what this means is a resumption of the purely sectarian assassination of Catholics, and it is hardly surprising in the circumstances that the ghettos are reluctant to totally repudiate the armed republican elements.

The way to resolve the undoubted ambivalence on violence is not to criminalise by association whole swathes of the nationalist community, from west Belfast to rural villages.

Just as there are demands that Sinn Fein should demonstrate its commitment to democracy and nonviolence, the political administration whose policies spawned and nurtured the militant republican rump must also acknowledge that its methods were crude, sometimes inhuman and too often elastic in their adherence to strict legality.

There is still no Bill of Rights in the North, in spite of periodic hints, half-promises and conditional overtures. There has been no political effort whatsoever to get to grips with the issue of disputed parades.

The vital issue of reform of the RUC has been fudged and pushed to the back-burner. A whole series of serious and authoritative human rights reports by the British government's own statutory advisory agency, SACHR, have been shelved.

This background of political neglect and negligence on basic issues of justice and equality is hardly a sensible basis for the marginalisation of republicanism.

The isolation of ruthlessly violent elements is indeed a desirable aim. It could be argued that the way to achieve it most effectively would be to draw the public face of republicanism more closely into the arena of political debate rather than drive it back into the confines of ghetto politics.