In Ireland, we’ve learned that debt is dangerous.  Debt is associated with half-built office buildings, negative equity, personal guarantees, Seánie Fitzpatrick and the IMF. The lesson of the last decade is that debt leads to personal and national ruin. Less often talked about is the benefit of debt. Used properly, debt can generate enormous wealth. And in this country, there’s no more artful practitioner of debt than Paul Coulson and the Ardagh Group. Ardagh is an example of what debt can achieve. Starting with one bottle factory in Ringsend, Coulson has borrowed his way to an empire of 56 factories with…