Much of what Whelan writes continues to hold a bearing on Sinn Fein's current dilemma:

For the IRA, and for many in Sinn Féin, the use of violence is seen as justified not only for ‘political’ purposes but also in the enforcement of internal discipline and in order to ‘police’ certain communities. As a result, for many in the IRA violence has become a way of life. The availability of such regular opportunities for violent activity inevitably attracts or generates psychopaths.

The crux:

The IRA also gives authority to local commanders over operatives and communities in a defined area and sanctions the use of violence to maintain control therein. In that set-up it becomes almost inevitable that some of those local commanders on occasion will deploy that violence in personal rather than ‘political’ disputes.