AFAIC, the "Trekkie" has always been a more juvenile distinction from "Trekker" (like a fan who just loves it, versus a fan who is more serious). But, if someone calls me either one, I don't really mind.
That's what "trekkers" tried to tell themselves, to look down on other fans as somehow more nerdy or fanatic about it, but it's a fake distinction made after the fact.
As others have pointed out, "trekker" was just invented because the term "trekkie" had come to have a negative connotation. Kind of sad that fans didn't just decide to stick with the original term and own it.