He was changing now, in rapid Chthonian, spells of containment and banishment. Nothing happened; the black smoke-mass came on inexorably, and now it was starting to have something of a shape—a malformed, enormous, hideous shape. (Prologue.22)
While a warlock summoning a demon is more like evil vs. eviler, eviler wins, bringing the score to Demons: 1, Angels: 0 before the book even begins!
"I thought gaming might have lost some of its appeal for you since…" <em>Since our real lives started to resemble one of your campaigns. </em>(1.2.84)
In the real world, "good" and "evil" only exist in games and movies. Clary never expected her life to turn out like one of these.
Clary still wasn't clear on who the bad and good guys actually were. (1.2.85)
We're not sure why she isn't. Valentine is clearly presented as evil to the reader at almost all times, and few of the other characters tread a line between good or evil. They all fall firmly on side or the other.
"What Valentine wants to do is reverse [the Sword's] alliance—make it an object of demonic rather than angelic power." (2.8.90)
Even objects in this world can be good or evil. In order for Valentine to change the allegiance of the sword, he has to commit a bunch of evil tasks to do it.
"It was a Drevak demon," said Luke, his voice grim. (2.11.114)
There are tons of demons appearing in the book. Not all of them have names, but all of them are gross and evil.
"Werewolves don't hurt people, or each other. Vampires are murders." (2.12.53)
Maia is (falsely) acting like werewolves are saints and vampires are evil here. By this point in the book, not only has she lashed out at Simon, but Jace got into a bar fight with a bunch of werewolves. Both races, were and vampire, are capable of violence.
"It's better to reign in hell than serve in heaven, etcetra, and so on." (2.13.66)
Jace is mocking one of Valentine's favorite quotes here. (Can you identify it?) Valentine is totally find siding with whatever side gives him more power.
"I'm no friend to demons," [Valentine] said. (2.13.86)
Valentine hasn't technically sided with the demons. He's just using them as pawns in his scheme. Does this make him good, or does it make him even worse than a demon?
"I thought we were all on the same side. I thought it was us against the demon worlds." (2.13.93)
This is how things would be if it were simple, but Valentine has to come in and complicated things, doesn't he? Cue some classic Avril Lavigne.
"The Angel blade burns you, just as God's name chokes you," said Valentine, his cool voice sharp as crystal. (3.16.182)
Maybe we were wrong. Maybe Simon is evil once he becomes a vampire. The Soul-Sword can only be touched by people, and it hurts Simon. But if Valentine can wield it, maybe the sword isn't that good a judge of character after all.