You've got to kill the person you were born to be in order to become the person you want to be.
I just LOVE that line.
If you watch it not so much as a serious biopic of Elton John (which it isn't) but more like a "Momma Mia" type movie set to Elton's music it has a very good "message" about the price of fame and finding yourself.
It's a great line all right! Because it encapsulates the process of developing a star persona, and tells that a loss of identity comes with doing so.
A lot of celebrities do the same thing, they pick a new name and develop a star persona, someone who's radically different from their original self, and quite a lot of them develop identity crises over time, or get frustrated because nobody knows their "real" self. And yes, since this movie is about Elton developing serious psychological issues over time, that one line both shows Elton his path and foreshadows his near-doom.