Yup ... They're scum ... but their HIS scum. Honestly, I would just be like ... 'Aye yo monsters, you can roll through, we won't stop you, do what the hell monster frickin' do' ... and just hole up in the guild with my harem.
Also, I do agree that he should help her to understand that her naivete will get her raped ... not that she hasn't been sexually harassed by ALL the monsters in the forest. I mean, it was explained that she emits a pheromone that affects monsters ... and from what I can tell ... the town IS FULL OF THEM.