I may be all wrong on this point but the little I know it sounds like Donatism all over.
Donatists argued that Christian clergy must be faultless for their ministry to be effective and their prayers and sacraments to be valid.
At least you admit you might be wrong.
Here is the definition of Donatism:
By denying the intrinsic efficacy of the sacraments the Donatists claimed the sacraments could be celebrated validly only by those in the state of grace. They required the re-baptism of any Catholic who came over to their sect.
Donatists had the outward forms of Catholicism, including bishops, priests, and deacons, Mass, and the veneration of the relics of martyrs. The heresy of Donatism lay not primarily in the denial of particular Catholic doctrines but in the assertion that only "sinless" men could administer the sacraments validly. The schism was effected by the rejection of the lawful authority of validly-elected Catholic bishops and culminated in illicit but valid ordinations of schismatic bishops, priests, and deacons.
No one that I know of is saying that Fr. Pfeiffer's Masses are invalid. The problem is that we are human beings, and subject to be affected by things like propaganda, errors, etc. It's not about Fr. Pfeiffer's state of soul or personal sins, but rather his public sins which affect his teaching of the Faith itself.
We are not saying "avoid Fr. Pfeiffer's Masses because he's a sinner" we're saying avoid his Masses
because he holds various errors, teaches distortions and propaganda in lieu of doctrine (according as it suits his cause), and is a scandal with his behavior towards other priests and bishops, which might actually cause YOU to sin by doing and saying things against these priests. So he is literally a cause of scandal or a stumbling-block. Not to mention his close association with a man like Pablo who takes scandal to a whole new level. It is not worth immersing oneself in such a milieu, not even for the Mass. The ends don't justify the means.
And then there's the issue of his promoting one Ambrose Moran, an evident con artist who masquerades as a Bishop. Since when are Traditional Catholics apathetic about the validity of one's sacraments? Isn't "seeking valid sacraments" one of the main reasons the Traditional Movement exists?
Say a man was travelling, and couldn't find a Tridentine Mass to attend on Sunday. What if a prostitute offered to tell him where you could find a valid Tridentine Mass, if he used her services once? (Let's assume he knows psychological tricks and can tell by her eyes, body language, etc. that she's telling the truth that she knows where a Tridentine Mass can be found.) Would the ends (attending Mass) be enough to justify fornication with a prostitute? I think not.