There are too many to list. If you search my contributions on these forums re the topic of Hell over the last few months, you’ll see them aplenty. But, let’s just stay within the limited scope of this thread regarding the angels. I don’t know how to precisely articulate the intrinsic dignity/value/worth of an angel. We use scriptural language to describe our own–we bear the image and likeness of God (which is a big deal). At least part of what follows from our own intrinsic human dignity, is something like Kant’s categorical imperative–you must always treat another person as an end in himself and never as a means only.
So, let’s consider this group of angels who fell. Were they created as ends in themselves? The natural end of an angel would be similar to that of a human, according to Aquinas, which is beatitude. However, on the classical, Western view of eschatology, the story is that God created these glorious beings (angels) with full awareness of their fate to be forever thwarted of their destiny–their beatitude in God. So, the questions entailed by this picture are quite natural. What kind of god would create doomed creatures who would never manifest their glorious destiny? It would seem that these angels are not treated as “ends in themselves” but perhaps as means to some further end. According to Aquinas, to love another is to will and work for the good of the other, as other (and not merely as a means to an end). So, how could it be be said that God loves these fallen angels? He created them knowing that they would fall and be irredeemable. That act seems to edge closer to what we mean by sadism than by love.
These are some initial thoughts, but they are enough. The classical picture in the West doesn’t seem to stand up to scrutiny, but maybe I’m wrong.