Knowing that you need to take action is different to knowing what action to take. It is a situation that policymakers find themselves in regularly – in Ireland and elsewhere. In recent weeks, Irish policymakers have decided that action is needed to protect the existing rental supply. The latest kite floated politically – one that seems to be sticking – is that all landlords, regardless of the size of their holdings, would be given a tax credit allowing them to pay no tax on the first fraction of their income. Before we get into the merits of that idea, think…