The tax system is extremely powerful, particularly in its ability to privilege one group above another. Sinn Féin’s Pearse Doherty has placed the issue of mortgage interest relief back on the national table for debate. The Minister for Finance has said he’s not for bringing mortgage interest relief for owner occupiers back. Several commentators, including UL’s Dr Ciarán Casey, have written about the scheme and how the return of the relief might work. Most have found flaws in the proposal.   Deputy Doherty’s specific proposal is to provide mortgage interest relief up to 30 per cent of the interest rate costs…