He's not human supremacist, just staying on the side of caution.
Considering how abnormal Akira already is + that 'giving skill' thing, he will be a major threat if he ever turn on humans.
There's also precedence of super OP goblin before that the humans are wary enough to make goblin slayer here (btw there's 2 other -slayer weapons, Dragon and Demon)
Also, that dagger actually kill on touch, in fact Akira instinctively felt [Death] from it so strong that he couldn't even grab it.