Some background on D. Slawson.  Doug was four years ahead of me in seminary.  He was ordained a Vincentian priest for the CM Western province in 1974.  (left and married)   He studied under and was mentored by Rev. Stafford Poole, CM, PhD.  Stafford is infamous for his in-depth studies and discoveries of what Bartolome de Las Casas actually said and did to protect indigenous people in New Spain (vs Church of Spain)  In addition Stafford's research and books on the *myth* of San Juan Diego - via Stanford Press - The Guadalupan Controversies.  
So, Doug has followed in Stafford's footsteps in terms of doing research necessary to address long standing *myths* and legends of the Catholic Church.  OTOH, their research has not really debunked but rather laid the groundwork to understand the context of the people of faith at that time and what the key meanings of these legends are.
Doug and I were colleagues for a few years on the Vincentian Studies Institute now based at DePaul University.