I really have to agree with this. Some of my favourite films as a kid had really evil villains. It is surprisingly reassuring when they meet a fitting end, and I find I am always nervous when an evil character just gets away and isn't punished. One of my favourite movie villains as a kid was Rasputin in Anastasia, a rotting corpse in limbo who often falls to bits. Some of the scenes really scared me, but I watched it time and time again.
I am a huge fan of del Toro's frighteningly beautiful imagination and was blown away by his imagining of the Goblin Market in Hellboy 2. I also loved that movie because the villain had an understandable purpose, trying to preserve the last magical creatures that humans destroy as "monsters".
"What's the biggest mistake people make in telling stories about children, or for children?