Being forced to kill those dragon slayers isn't meant to be an RP choice. They hate you because you are a dragon, which is also something forced on you against your will. There's no option to rejoin them because no matter how much YOU wanted to, THEY only want to see you dead. That is their mission, and that is what they've been indoctrinated for years into believing.
SPOILERS FOR A BIT LATER IN THE GAME!
The only dragon slayer in the game who seems interested in understanding you and learning the motivations of dragons is Kenneth, one of the Battle Tower servants, and even he's only willing because he's magically bound by the Island to be willing. He has no choice, his refusal will mean his death, and if chosen, he is probably bound even further to be unable to attack or kill you.
So basically, as long as you're a dragon (regardless of whether you wanted to be one or not), the dragon slayers are your mortal enemy and want you dead.
