Blue,
I appreciate your view, but honestly, what possible requirement is there for fast jets in Ireland? Or "interceptors" as the post asks? To intercept what or whom exactly? Why spend a farthing of the hard-earned defence budget on something unnecessary, let alone a huge percentage of any defence budget on something utterly unnecessary?
As for the PC-9's, they are a superb trainer and their purchase was a wise move, but 8 is probably two too many for the training role, and arming them is just an embarrassing fantasy. Granted, armed PC-9's have some utility as live CAS trainers for troops who may need to work with CAS assets from other countries when deployed, but that's a pretty thin reason. Deploying troops need to know how to direct precision weapons - LGB's, JDAM's etc., and armed attack helicopters - not fixed wing iron bombs, .50 MG's and rockets. Better and cheaper to send folks to a real CAS FAC course with EU battlegroup partners Sweden and Finland, or with the UK, NL, Canada, etc.
Yes, the PC-9's would be effective CAS platforms in places like Liberia or the DROC, but only after getting lots of kevlar armor and flare dispensers as a minimum.