Thank you all for your replies. To be honest, I remain puzzled by Fellay's concluding remark. Can any of you tell me what SSPX says is the raison d'etre of Tradition? Is this a matter about which they claim some sort of special knowledge which, on their view, Rome lacks?
"Is this a matter about which they claim some sort of special knowledge which, on their view, Rome lacks?"
Not lacks, rejects.
Have you read Saint Pius X on modernists? SSPX holds that the modernists continued what Pius X saw them doing, and by the middle of the 20th century had gained enough influence to steer the Church away from authentic tradition.
Think of it as similar to the way leftists in America have gained ground step by step, until now we find ourselves completely divorced from the principles on which the country was founded.
After all, leftists and modernists both take their marching orders from Satan.
The schism was solely about the disordered will of Marcel. His error about Tradition was the intellectual rationale (whioh was the defense mechanism shielding his ego from the truth about his perfidy). His memory was poorly functioning at the time of his schism, so poorly functioning he was, hopefully, and likely, not culpable for his schismatic acts.