The evil I refer to is the idea of taking pains to commit random, motiveless murder of a helpless innocent victim for no reason other than to do it.
Most murders have a highly relevant and particular motive to the murderer. Even terrorism has a motive, but to achieve that motive it must have a broad reach. Hacking a medical connection to kill one person won't achieve that.
Yet surely, someone would do it just to prove they can.
You might say a terrorist would want to do it many times over because that would be effective. But I counter that doing it just once would lead to the closure of whatever loophole he exploited; to continue any further would be an expensive cat and mouse game. No terrorist sees the ROI in that. So it's a dead end.
So, in reality, what we're looking at —as the only viable scenario— is a sick loser who wants to incite disgust and sorrow.
Hence, "never underestimate people's capacity to be mind-blowingly evil".