There would be some sort of argument here if passengers using Belfast were being asked to pay at least 19 euro per head which is charged at DUB before the 3 euro tax is added on.
The package holiday market from Belfast won't suffer at all as last summer it was cheaper to fly from Belfast on package holidays because there was so much more capacity that out of the South. Two weekly flights to Enfidha next summer a prefect example, DUB can just about support a weekly service for the peak summer. If NI scrap the tax it won't make any difference, new airlines won't flow in. One very big problem for the North is social unrest which makes news around the world every few months and of course Belfast will suffer because of it.