Every country uses it natural resources as best it can to meet its needs, human resources, agricultural resources, whatever.
Ireland's geographical location gives us a temperate climate, and little threat of foreign aggression from any external power except the British.
We have finally (I hope its final) resolved the UK situation, a military response to our defence requirements is nonsensical. We do not have the population or the militarised society to militarily resist say a US invasion, but we do have the political positioning to make it extremely unlikely. (Compare our situation with North Korea, they have built a military defence to deter the threat of US invasion, lucky them ! )
The British also provide us with a military defence against any other possible agressor. Not out of love for us, but in their own vital interests. They are not going to allow Russia invade Ireland.
To spend money on a military defence where little threat exists and in the unlikely event that a threat did materialise we could not counter anyway, is foolish.
We do take responsibility for our own defence, we recognise our extremely fortunate geographical position, we recognise that it is in our nuclear armed neighbour's interest that no foreign power be allowed attack us, we build deep political and trading relationships with our neighbours.