Back when the churchmen were sane, pre-VII, the Index was a very good thing. One didn't have to question whether one should obey the Index, because the books which were banned were all anti-Catholic, critical of the Church, or against the faith in some way, or subversive to it.
Now, it would probably still be a good thing, because the liberals would not dare to use the "absolute truth" authority of the Church to ban books of traditionalists. They would not ban books today, for the same reason that they suppressed the Index Librorum Prohibitorum in 1966, namely, they renounce their authority to tell the faithful what is right and what is wrong.
Essentially, one might say that pre-VII, the Church could do no wrong, because it was Catholic through and through. The Pope was a proponent of the traditional Catholic faith, the Sacred Congregation of the Index, charged with the maintenance and upkeep of the Index Librorum Prohibitorum, were "trads."
Bad books will destroy souls just as fast as bad companions will, perhaps moreso. Censorship is a good thing, but it must be Catholic, not modernist. It is a great pity that the index is no longer updated and enforced, because I believe that many more works of the modernists would be condemned than would works of traditionalists. It was a weighty matter for a book to be put on the Index, and not done lightly at all. Thus, only books contrary to the Catholic faith made it on, and not books which were simply critical of one Bishop, unless the ramifications of this criticism could do grave harm to the universal Church. There is much contrary to the Catholic faith in the works of the modernists, and nothing contrary to the faith in the works of traditionalists. Consequently, if the Index was administered rightly, all would be fine.