In a conference given by Fr. Joseph Pfeiffer on Saturday August 31, 2013 in Levis, Quebec, he explains again and in a bit more detail how the first condition, officially determined by the 2012 SSPX General Chapter as essential prior to a canonical regularization, offends the Faith and is therefore morally unacceptable.  The relevant extract (14 min 0 s to 17 min 50 s) of that conference is below.

Two previous postings on this matter are here and here.