Except there's no way for the Unicode standard to be prescriptive enough for the different implementations to express identical intent. And that's before the politics get mixed in (e.g. Apple's water gun). That's why you see many chat services and social networks shipping their own whole and opinionated emoji font: at least on their platform every user sees the same glyph and although there is still room for interpretation and misunderstanding, that's not by having too many font designers.