(The mindset of : Death must be avoided at all costs)
Children most likely dying in the orphanage due to childhood illnesses such as smallpox would have backed up his point of wanting to surpass passing over. (He would have thought it as weak)
During WW2 people died / Hitlers rule partially impacted his decision to be immortal.
He goes to an extent of separating himself from his father. He made that conscious decision to get rid of his good looks and become something terrifying. (Hence the snake like appearance: linked to slytherin)
He shed his lineage like a snake shedding its skin
He used his looks for his own benefit
Hepzibah Smith's death was sealed when she bad mouths (offends / criticise) his mother ? Or he killed her because he is desparate for what he thinks is rightfully his (the locket) out of greed
Things connected to him is just as majestic in his eyes: e.g. the gaunt ring
He is reminiscent to a leech
Cold, calculating, intellectual
His appearance started to match the distortion of his soul (dorian gray situation) he chose to be on this path.
Some of his followers were raised to believe that he had the right ideas e.g. Draco, Lucius, Bellatrix etc.