Luckily, I saved this post someone made for just an occasion.
>Many have heard that becoming a lich is inherently an evil act. Details, however, are rarely discussed. After all, publicizing the details of necroapotheosis would be nothing but a boon to those considering the dark path.
First, it is essential to understand what we mean when we talk of "negative energy." Is it energy, but inherently destructive? Naturally not. Many kinds of energy are destructive. Is it the opposite of life energy? Well, while that's almost correct, it's not a very informative phrase. Doesn't mean much, "opposite of life energy."
No, there's a simpler, more accurate way to express it. "Negative energy" is energy passing out of the world. Like water flowing downhill and driving a waterwheel, power is generated when life flows into death. This is why many undead actively feed upon the living; it is life force, extinguished, that gives them power.
All undead are powered by negative energy, and so all are powered by the annihilation of living anima. Some seek and harvest actively; vampires, for instance. Some are passive... the tiny deaths of grass, distant animals, and the tiny creatures that surround us are enough to sustain the flow through the black hole at the heart of a mindless skeleton.
Liches, then, are something of an anomaly, no? For, with a few exceptions, the more powerful an undead, the more likely it is to actively feed... mere flesh for a ghoul, living blood for the parasites, and souls themselves for the great Devourers.
How, then, do liches feed? Cleverly. Automatically. The process is active as long as the phylactery exists, and once set in motion the lich never need concern himself with the details.
More specific? Let's just say those who suspect lich activity should keep an eye on infant and child mortality statistics.