As someone who was also wronged by his home city, he understood the proselyte's feelings.
In order to appease the Supreme House and not be abandoned, slave cities are willing to do, absolutely anything for the better good of many. Even if it would be unfair to one person, the city only viewed the well-being of the majority.
Reality often worked like that.
Had it not for the deal he made with Professor Victor, Lucivar might've let him go.
Killing the proselyte is barely a reward for Lucivar so there's no point insisting on killing him.
But with his life on the line, he couldn't let the proselyte go.
And the more he thought about it, the more that it was fate for the proselyte to die here.
'Even if there's no deal, I'd probably kill him for choosing evil too...' Lucivar shrugged.
It was unfortunate, sheer bad luck—Lady Luck spat at the proselyte and placed him here.
So there's no other outcome for him other than death.