They werent, thats a myth.
The early IRA were terrorists, and did target civilians. In 1916, 1918-22, and people completely forget the bombings on mainland Britain by the IRA just before WW2. The idea that the early IRA were somehow morally different to the IRA of 1969-today is frankly a nonsense.
The modern IRA has simply been better armed and more efficient.
I have never been a fan of the IRA although, as I said, some of my ancestors were part of the 1916 Rebellion (or so they said!) I didn’t want to call them terrorists as well as a pretty sadsack army, simply to avoid being flamed!!