That's the beauty of a role-playing game: the freedom to play what you like. If you want to be a psychopathic serial killer, go for it.
That being said, it's important to note that SR DOES take pains to point out that, while runners are not "Good guys" usually, if ever, that Blood Magic, Twisted Paths, Toxic Paths, and Insect Totems cross into a degree of sick-mindedness that is reserved for NPCs or the most indulgent of GMs. And even if that WASN'T the case, each of these exacts a toll on the soul and psyche of it's user. Blood Magic stains you, metaphysically. Twisted Paths are addictive and hard to crawl out of. Toxic and Insect are violent and self-motivating: they are not motivated by freedom or profit, but zealotry. You loose your freedom to your cause, which inevitably involves the extermination of the human race, whether to save or kill the earth, or use them as hosts.
Always remember that that darkness has a price. That's all the rule truly says.