I don't think fear of judging the pope is based on the universal admonition against judging souls, but rather on the specific admonition of Pope Innocent III "he (the Pope) judges all and is judged by no one."
Of course, Pope Innocent said this in a time when Catholic laymen were blessed not to have electronic media that gave them access to every papal "off the cuff remark" and personal impropriety (which no doubt would have caused disastrously widespread scandal during the pontificates of say, Stephen VI, John XII, or Alexander VI).
The pope was someone the average Catholic never saw, and could not even pick out of a lineup. The pope was the Vicar of Christ, whose name was remembered in prayers, and that was about it. The duty of the Catholic layman was salvation of his own soul, building up his personal sanctity and developing his Sensus Catholicus. At times that proved difficult (the Arian crisis of the 4th Century and, well, the Modernist crisis of today come to mind), and during the Western Schism, laymen could not even know who the pope was for close to a century... But the layman's duty remained the same, as it remains today.
My own view on the "option" of Sedevacantism (which is de facto lay judgement of the pope) is identical to Bishop Williamson's (as I quoted recently in the "Would you follow him" thread). To paraphrase: We Catholics had been spoiled with a century's worth of good popes before the crisis hit.... And now we're finding out (thanks to electronic media) just how far astray Christ will allow the head(s) of His Church go, while still not allowing the Church to cease being what it has always been.
And this may be apropos of nothing at all (or it may not) but most of the sedevacantists I've personally known have been converts from Protestantism.