The IRA is doing it for political reasons and not religious which is what the point of this thread is. Their targets are politicians, police, and non-supporters of their cause, not just someone who is of a different religion.
Missing from Vorticon's list are examples like:
The Tullyvallen Orange Hall Massacre, 1975. 2 IRA men walked into an Orange Order (a protestant group) hall and shot dead 5 people.
The Kingsmill massacre. Ten protesant workmen were in a minibus on their way home from work in a textile factory. The IRA had set up a roadblock on the country road they were on, and forced the minibus to stop. The Catholic driver was told to run away, the ten workmen were lined up at the side of the road and shot dead.
The Darkley hall massacre. INLA gunmen walked into a Pentecostal church service on a Sunday and shot dead 3 church elders.
There are scores more, mostly involving just 1 or 2 killings.
Also, there's the Claudy massacre. Whilst not strictly a sectarian attack, (it was a series of bombing of a small mixed Catholic/Protestant town), it's relevant because the IRA gang that carried it out was led by Father Jim Chesney, the (Catholic) priest of a neigbouring parish. (9 people were killed in the Claudy bombings, including 3 children, one of them an 8 year old girl)
The Republican terrorists sought a united Ireland. Because the majority of Northern Ireland is Protestant, and wants to remain part of the UK, they sought to drive out Protestants by killing random members of the community. (The Loyalist terrorists did the same, of course)