I will certainly not enter a cesspool like Reddit for such as discussion...For anyone trying to place a judgement on whether instrumental music can offend the listener, What gives you the right to judge another person's belief system? Would it not be better to seek understanding of someone's belief rather than condemn that belief as irrational? People can and do go the extreme on any topic of discussion. See Discussion threads on Reddit regarding Occult Classical music.
As someone already wrote above, some people nowadays will be offended by anything.
We had once supposedly reached a stage with most adults going by the maxim "...but words can never hurt me". This has been almost reversed. Language has to be policed, we need warnings for all kinds of arts and literature (far beyond horror, violence and sexuality where there might be some rationale for such warnings), all kinds of censorship creep into schools, libraries etc.
Nobody is forced to listen to classical music (unlike some popular music one can hardly escape when shopping) and very little has a obvious connections to the "occult", e.g. none of the Strauss and Rachmaninoff selections in the first post have that (The Isle of the Dead is basically a graveyard, like the funeral isle in Venice, there is no reason to assume that any necromancy is going on there).
As we have also already seen there is far more opportunity to be "offended" by religious music, even if half of the text is taken straight from the bible, as in the "Ave Maria". Again, unless one lives in a very catholic area, it seems unlikely that such music would be forced on someone.
So overall, I do think there is reason for judgement here because the exaggeration of sensitivity, i.e. being very easily offended, is something overall bad for almost everyone.