The briefcase quest doesn't make you a slaver. Joining the slavers is the only way to become a slaver.
Oh really!? Thats great but the wiki said it differently..
"Rewards
A fully loaded shotgun and 20 shells.
Some caps (according to your charisma).
800 xp (from Metzger)
1500 xp (from Little Jesus Mordino).
Your reputation will increase by 150 points with slavers, decrease by 200 points with Regulators and
people will consider you as a slaver."
Is the wiki wrong?