The long and short of it, if that for many people in Dublin, there is no reasonable, viable alternative to using a car. The public transport infrastructure isn't sufficient, and isn't reliable enough to depend on.
When I lived in Ireland it would have been impossible for me to live comfortably without a car.
However I now live in continental europe, and am perfectly happy without a car, since there are real alternatives. Where I live, the underground network allows you to go to any part of the city quickly and reliably. The buses are very frequent and run to schedule. My monthly ticket for all buses, underground, surburban trains is less than 40Euro.
However in Dublin, for example going to work, I had the choice of a 40 min car journey, or 1 hr 30min commute on public transport. Its all well and good to say that people should make sacrifices (in my case 50mins of my time twice a day) for the sake of altruism, but that doesnt wash.
When I changed jobs, I was very fortunate to be only 20 mins walk from work, so didnt need my car for my daily commute, but was still invaluable in making longer journeys or for picking up groceries from the shop which was a few km from my house.
When I move back to Dublin, I'll immediately get a car, since I know a real alternative does not exist.