In my opinion, the Donatistic conception of ecclesial authority is one of the primary factors hindering ecclesial unity. According to this conception, ecclesial authority is contingent upon one's own determination of the moral or theological qualifications of the individual holding some ecclesial office; and if one determines that the particular ecclesial authority does not meet those qualifications, one may justifiably 'rebel'. (I discuss Donatism, along with Montanism and Novatianism in "The Gnostic Roots of Heresy".) This Donatistic conception fails to recognize the sacramental nature of ordination, instead treating ecclesial authority as if this authority is derived democratically, from the bottom-up.
Last month I mentioned in passing the way David treated Saul, and what Jesus says about the "seat of Moses". Recently I read Jonathan Deane's post titled "The Stone Caster". He brings out very well the implications of Christ's words about the Pharisees in the "seat of Moses" for a Donatistic conception of ecclesial authority. Here's the link.