Just to be clear, you believe that someone with an Irish passport who lives, say, in the U.K. should still pay Irish taxes in addition to U.K. Taxes? Or is it that once someone leaves Ireland they're stripped of their citizenship?
The US is actually the only country that I'm aware of that takes the former view, and it's generally regarded as pretty pointless.
Well, the US view is that you should pay up to US taxes somewhere. So if you pay tax in Ireland, for example, you are paying more than US tax would tax, so your liability is nil. Yet you are afforded the full protection of the US state.
Personally, I have no problem with world-wide income being taken into account, at least at the rates the US charges. If you point me at Irish tax rates from the nineties, I'll have a different view