^ Please explain why she killed that fortuneteller in chapter 25. He claimed he wouldn't do anything to harm other human but she killed him without hesitation. Are you saying only people who she knows can become a youkai and the rest will be dealt with like the salt mansion owner from chapter 37? Why did Yukari even had to intervene to help Kosuzu?
I think Forbidden Scrollery established the fact that a human turning in to a youkai is the greatest sin there is in Gensoukyo and that Reimu deals with that issue as soon as she notices these things, whether she likes it or no.