Economic theory says no such thing. It is true that investment might reduce if taxes are raised if ceteris paribus, but as tax rises either increase revenue or reduce national debt, they are never ceteris paribus.
Imagine we had very low taxes, but the state did not build roads (so transport costs went up), provided only minimal policing (so companies would have to spend more on their own security people) etc., it is far from obvious that it would be good for business in general.
Ireland is increasingly annoying not just the US, but other EU countries, and many others. It is also subject to EU law, and its economy us currently very weak, making more dependent on the rest of the EU.
Incidentally, Warner Chillcot was originally a Northern Irish business (Galen) that changed its name to that of an American company it bought.