Sure that story is popular before the Author move it to another site. Shit’s getting wacky around the Community.
I’ve read the story that it does kill Mamono. But that doesn’t mean it is justified to transform humans into monsters and try to make him into one of their own. The guy had witnessed the horrors of Yharnam and people subjecting themselves into slaves to the Illusion of Monster Love. For him is as worse as to be a Bloody Beast.
That person in the story, Cyril, wanted to be alone in peace.
This is how I sum up the story. Just saying.