I've been reading the fantastically well researched book by David Berresford called Ten Men Dead: The Story of the 1981 Irish Hunger Strikes.
One Stirring passage reads:
"Hunger-striking, when taken to the death, has a sublime quality about it; in conjunction with terrorism it offers a consummation of murder and self sacrifice which in a sense can legitimize the violence which precedes and follows it. If after killing or sharing in a conspiracy to kill-for a cause one shows oneself willing to die for the same cause, a value is adduced which is higher than that of life itself. But the obverse is also true: failure to die can discredit the cause. To scream for mercy at the foot of the gallows or nod at the saline drip as kidneys and eyes collapse and the doctor warns of irreversible damage—is to affirm that there is no higher value than life and none more worthy of condemnation than those who take it."
I'll do my best to answer this but I'll have to go outside the 80s to mention relevant factors from earlier in the conflict.
The early 1970s saw what we now usually refer to as the "insurgency phase" of the conflict. The British Army felt this ended by 1972 but it's clear looking at the casualty figures that the earliest years of the Troubles were the bloodiest.
Various names have been given to the time after that, the long war, the terrorist phase etc. British officers used to joke about "an acceptable level of violence" but you see a drop from over 12,000 shooting and bombing incidents in 1972 to less than 3,000 by 1977.
British intelligence activities meant that the IRA had reorganised for the most part to a cell based structure by the late 1970s (a notable exception being in South Armagh). They were a lot harder to infiltrate but it also meant that there was less contact with the civilian population and cells could operate a lot more autonomously.
Though it was not the reality, civilians were not meant to be a target. Bombs planted in civilian areas were not intended to kill large numbers of non-combatants but instead disrupt economic life in Northern Ireland. This was also why phone warnings were typically given although the cryptic nature of these generally resulted in more confusion and in some cases, the civilians evacuated closer to the bomb. The IRA realised the negative publicity they received from civilian casualties but it wasn't enough to deter.
The IRA maintained that its campaign was focused on the British security forces and not the predominantly Protestant unionist/loyalist population but sectarian killing occurred throughout the conflict. A lot of these were 'tit for tat' killings where the murder of a civilian by one side would see revenge attacks occur. Massacres such as Kingsmill were so horrifying that by the mid 70s leading republicans and loyalists agreed to a halt on random sectarian killings though this would be broken in later years.
Then there's the murky ground of what the IRA considered a civilian. The IRA did not view past members of the police or army or loyalist paramilitaries as such. Politicians, judges, prison guards (past and present) were also considered exempt from this. By the early 90s, even civilian contractors working with the RUC or British Army could be targeted. Informers were also seen outside of this rule. Anyone suspected of leaking information to the security forces or otherwise could be executed.
So in short, civilians weren't the target (in theory) but in practice, this did not work out and many of them were killed. There were also numerous civilians killed in what the IRA viewed as justified circumstances (like those mentioned above)
Sources:
Provos/Loyalists/Brits - Peter Taylor
3-2-1 Bomb Gone - Steve Smith
The Dirty War - Martin Dillon
A Special Kind of Courage - Chris Ryder
Bandit Country - Toby Harnden