Morbid poetry typically involves self-harm and suicide, harming others and murder, disease/plague, among many other unpleasant things, and it generally makes it disconcerting to anyone who may read it. It also kind of shows that the writer, if they're trying to convey their feelings, has serious mental/emotional issues and might need major help. It helps no one if someone even remotely caring gets their hands/eyes on the poems/songs/artwork.
Yes, it can be better than drugs, but it can be just as harmful from an emotional standpoint. Having the poems around means the writer can brood over them, and they can start feeling even worse, and that can reflect itself through physical acts and changes in behavior.
Personally, I get rid of my anger/depression primarily through games. (I don't mean Call of Duty and the like, since other players can exacerbate the problem.) Changing up a team in Pokémon and maybe beating the Elite Four when it seems like I have a disadvantage is really satisfying, because I'm actually overcoming a possible challenge. Maybe getting through an annoying boss fight in a different game, or just feeling the fun of starting a game that hasn't been opened yet. Listening to happy, upbeat music (regardless of genre) does a lot of good, too, since it's difficult to stay angry or sad while listening to it.