I used to find it difficult to understand the fall of angels. Living in Heaven in the presence of God, why would they rebel and become demons?
I now find it easier to comprehend, since I regard each angel as an individual, and some are evil by nature.
More exactly, I don't regard angels as a separate creation from Men - but as pre-mortal Men, as pre-mortal spirits. And all Men are agents - have free will - since each has existed from eternity, and has a part of him that is uncreated, divine, co-eternal with God.
In other words, before we became part of divine creation as children of God, we were already beings; and like all beings were alive and had consciousness and individuality.
I regard the goodness of God as a project, into which God hopes to bring as many as will willingly join. But as some men were made children of God it will sooner or later have become apparent they wanted no part of God's plan of loving creation; and of these some were actively hostile. It was these actively hostile spirits who became the demons; and whose motivation is the destruction of creation.
(I suppose that there are also pre-mortal spirits who simply opted-out of the scheme of creation - and dwell eternally alone and inactive.)
God loves all the children, including the demons; and administers creation thus. It is not possible, in principle, to summarise how this works - because every single one of God's children is an unique individual, with an unique disposition and motivations; and all are agents, able to choose.
But some choices are irrevocable (because true agency entails that we can make permanent choices). So God's creation takes all of this into account.
It is well to think of this symphony of unique and free voices - good, evil and indifferent - that constitutes creation, when we suppose that we have detected some contradiction - or unlovingness - in the world as we perceive it.