One of the first things that a paramilitary organisation learns to do is to impose discipline on the community within which it operates. It may rationalise this as "filling a policing vacuum", or representing the will of the community, but they all do it.
And if there had never been a rift between the RUC and the Catholic community - much exacerbated by IRA attacks on police officers - the IRA would still have kneecapped young delinquents and sex offenders, just as the loyalists did in areas where the police were not estranged to the same degree; indeed, loyalists were often heard referring to the RUC as "our police force".
And today dissident republicans continue to shoot perceived offenders, even though the police service is now accepted by the broader republican community, and has been since January 2007 when Gerry Adams first called on those who had evidence against the murderers of Robert McCartney to report it to the PSNI.
There are several weaknesses in the "policing vacuum" argument for community vigilante attacks on criminals. One is that practically all of those shot or subjected to horrific "punishment" beatings had already been dealt with by the police.
True, many of their victims were dissatisfied with how the law had served them; people getting short sentences or acquittals, but complaints like these are common all over Ireland and Britain. Policing is never perfect and just isn't vengeful enough for many.
The thug who stole your car or beat up your brother gets three months in a young offenders' centre; you think he deserves more and there is a neighbourhood vigilante who will do his knees for you.
Here we had political arguments erected in defence of this and even social service interfacings with the vigilantes themselves, but that doesn't change the basic core of the system.
A clergyman is reported in the papers to have been caught importing homoerotic pornography.
The UVF see him, absurdly, as a danger to children, decide that he hasn't been punished enough and beat him with nail-studded clubs, the preferred weapon of paramilitaries on ceasefire. He dies. The Rev David Templeton was killed for being gay.
John Collet in Derry, a known sex offender who had already been prosecuted, is kneecapped in his home by Provisionals using a .38 Magnum, a larger-than-customary pistol, and he dies five days later.
Well, that is what a lot of people would like to see done to paedophiles everywhere when the alternative is a sex offenders' register, lifetime monitoring and the prospect of offending again. Within the Provisional IRA there were senior members in Belfast who argued in the early-1980s that something had to be done about crime.
Busy criminals were drawing the police into the area and this was disrupting IRA operations. They also argued that the skills of the criminals could be put to the service of the IRA. If they were good at stealing cars, they could steal for the Provos.
Several criminals were made to sign amnesty agreements with the IRA.
In these agreements the men undertook to give up their criminal careers and accepted that if they went back to them the IRA would have the right to "execute" them. Three were executed under that initial scheme.
The primary interest of the Provisionals in that management of crime, therefore, was to clear space for their own operations. With the evolution of Sinn Fein came the development of the old republican theory that you can compete with the institutions of the State by replacing them.
Sinn Fein advice centres, like Connolly House on the Andersonstown Road, acted as de facto police stations where people could lodge complaints against local criminals, mostly car thieves. And IRA men operating from the same building would investigate the complaints and kneecap the offenders.
It was a parody of policing rather than a substitute for it, for, if your car was stolen, you still had to report it to the police to get your insurance payout.
Usually a kneecapping was a bone-breaking leg wound below the knee, sometimes in both legs, sometimes also in the ankles. The IRA expended more bullets into the legs of local teenagers than into any other target in the 1980s and there can be little doubt that this was popular with many people.
It did not, however, end joyriding. The joyriders themselves began to feel that they were at war with the Provos and went out to taunt them. Some were the sons of Provos, playing out a generational conflict on the streets.
In recent times, with greater disclosure from former IRA men like Brendan Hughes and Eamon Collins about the evolution of the IRA campaign, another possible theory emerges for why the Provos put so much energy into chasing car thieves.
This vigilante activity was a way of diverting Provo energies at a time when the war was being secretly wound down.
In the mid-1980s, after the importation of a massive arsenal from Libya and some bellicose statements from the IRA, many members expected an escalation towards a "Tet offensive". It never came and more members were deployed against joyriders than against the Army and the police through a section of the IRA called "Civil Administration".
Civil Administration kept the gunmen busy while the leadership got on with developing political activity and ultimately the peace process.
None of this explains why the current crop of dissidents wants to be vigilantes too, and shoot young offenders in nationalist communities, when they are pledged, publicly, to directing their energies at the "British occupation".
One simple part of it is that if they can't actually kill police officers or soldiers, they still have to be visibly busy with guns, or they will be forgotten and ignored.
In the same way the Provos turned their guns on alleged drug dealers during the ceasefires, when the peace process got shaky.
When you can't risk shooting a policeman, but you want to look dangerous all the same, you shoot a neighbour.
And another part of why the dissidents want to shoot criminals is to extend their reach within communities among those they serve in this way and those they implicate in their secrets.
Once people report offenders to them and men are shot, then the conspiracy is widened and return favours are due.
"We shot that scumbag for you, so the least you can do is mind a couple of sports bags for us."
It may not work exactly like that, but it is easy to imagine how it could.
And it is easy to imagine, too, how those who have used the services of the paramilitaries will prefer to justify what they have done and blame a policing vacuum, or the British occupation, than accept responsibility.