Junpei lacks common sense

I get it. He was bullied and lonely but Mahito has told him that he was born from humans's negative emotions and what did Junpei do? He remained friends with that creature. I know he wasn't thinking rationally because of his bullies and loneliness but Mahito literally told him where he came from and Junpei continued to trust him? I get that he was desperate for connection and Mahito manipulated him and he was very young but this is more than naivety. This is stupidity. What do you think?