Serious Love (not the kiddy stuff)

In Harry Potter, love is treated as a branch of magic because let us not forget that Harry's mom died to save her son. (and NO for anyone who wants to compare her to Jesus. OPEN YOUR MIND, kthx) Love is an important theme in the books, and it is implied that it is Voldemort’s inability to understand the concept that leads to his eventual downfall. (SPOILER ALERT) Since he does not understand the selfless love contained in Lily’s sacrifice, he is unable to predict the consequences of Harry’s own sacrifice at the end of Deathly Hallows.

It is implied that the inability to love is what make Voldemort as evil as he is. Severus Snape, who voluntarily joined the Death Eaters on leaving Hogwarts, turns spy for the Order of the Phoenix when he realises that the woman he loves is being threatened by Voldemort.

Narcissa Malfoy’s love for her son Draco eventually leads her to betray Voldemort, directly leading to Harry’s survival– another oversight on Voldemort’s part. 

With these examples, the book strongly hints that anybody with the ability to love cannot go as far down the path of evil as Voldemort has done, and it is his complete lack of compassion that makes him capable of what he does.