>>38472658It's rare for a human and a monster to have human offspring, guaranteeing a drastic reduction of human population in one or two generations, leaving human communities as easy prey for the hordes of monsters to conquer and subjugate and eventually to extinction; which would also lead monster girls to extinction because they will no longer have the mediums to generate offspring.
Luka's plan is foolish, didn't think on the long term consequences of his actions because muh snek waifu and Ilias did nothing wrong.