The answer is that intention is closer to motive, the idea that there was a special inducement to commit the crime. Motive, considered along with Intent, help us easily distinguish harmful consequences from blameworthy and non-blameworthy accidents. Negligence is a blameworthy accident in which a person didn't exercise a reasonable degree of care. Negligence lacks a motive, however, and the only defenses to it are mistake and justification. Justification is the more important concept.
Intent is always selfish, and it's never sloppy.
The person knows what they're doing. They are cunning and trying to be clever. Think of it as the sin of arrogance, or excessive pride, so to speak. Or think of it in terms of community expectations. The problem with Intent and the Law of Homicide is how to individualize it.