I find it very disturbing how people sympathize with the Joker, and this is coming from someone who used him as an av for 10 years and he is my favorite villain of all time. You even seem to find love for him.
The Joker is a complete psychopath. He has no emotions for people, and everything is a game to him. He sees people as prey, as pawns, as pieces on a movie set to be used, abused and moved around for his own amusement. He is in a way, worse than evil, as an evil person can at least be sniffed out through simple eye contact. The worst part about pure psychopaths is you can't even tell that they are psychopaths. They hide the normal emotional and facial expressions we all know and are able to read. Sure, the Joker makes a mockery of this, with his clown make up which actually accentuates his face at times, especially the laugh and smile (The Climax of his pure Joy from pulling one over on people) it still slides by a lot of people.
Like most legitimate psychopaths, the Joker is extremely charismatic, through this he is able to play people, against themselves, against others, and even for just his own tricks. He is the most dangerous type of criminal type, and it's right in everyone's faces. No real motive, no objective, pure chaos encapsulated.