He most likely considers all the witches victims, including those who are out to kill their own kind, maybe even more so as they would be the saddest sort. The witch at the factory would have just reinforced that feeling. He'd not be incorrect at all by thinking so. I imagine there are a bunch of witches so batshit crazy, as a survival strategy, they wouldn't anymore fit the bill, but so far Ryouta hasn't fortunately encountered one of that kind. He's already taking care of 4 very different witches, and especially his beloved Neko could have been used as an assassin against her will, just like this witch he chose not to slay. In short he has much sympathy for the witches.