I think the small car is a good idea for several reasons. One is since presumably you have to meet a flight on the way back, it gives you the elasticity to meet that schedule, if you make a mistake, get injured, push you itinerary, have horrible weather, you can in an hour do a day's cycling distance by car. On a short trip with deadlines that is actually pretty smart.

Second, having lived off and on in Ireland, I have been there in droughts, and in torrential, cold, sideways, rain. Maybe not the same day, but you never know. You could easily get 7 days of weather where cycling was something only a fanatic would do. You could adjust your plans or even go to a different part of the place where the weather promises to be better, if you had direct access to a car.

On the righteousness point: 1) the flight over will burn so much gas, but apparently you don't get kicked off the couch for that; 2) Been a while since I lived in Ireland, but the pollution profile of their cars was way worse than over here, belching black smoke. Clarity starts at home; 3) nobody would say anything if the guy was going on an organized tour with car support.

I do agree based on living in Ireland, that a big American style SUV is probably not a good choice. A small car that slips through the narrow roads is all you need, and you didn't have to used to worry about people in Hummers running you down on the way to the Big and Tall store. But there have been many changes in the last 10 years, so I don't know for sure.