As Matthew spoke of deserving to die horribly, Stephen's expression grew progressively more disgusted, though there was a definite note of pity in his voice when he spoke. "So what you're saying is...I should just kill you right now because you think it's what you deserve? Or you think it's what you want?" That one part of it rang through him as he stared at Matthew. He smiled a little. "Then you're asking me to grant you a favour. You want me to help you run away, ultimately."
He snorted when Matthew mentioned the wards around his house. "I know how to get through your fucking wards," he said, "I did it once without even taking them down, I can do it again. You have three and they're nothing I'm not experienced with. But I think this time I won't mind being a little bit destructive. I mean, I won't take down the Muggle-repelling one, but don't think I have too many qualms about leaving your house open. If anything, it'll make things easier for you - they'll know you didn't just run off and throw yourself into the Channel." Stephen wasn't the sort of person, kidnapping his former friend or not, who would take slights against his talents.
When Matthew insisted being buried alongside his kin, Stephen gave him a rather uncaring look and replied, "Well then maybe I'm crueler than you are, me being one of those inherently immoral Mudbloods and all. If you die I might let them find your body. But in any case," he smiled wickedly, "You've convinced me that the worst thing I could do to you is keeping you alive, seeing as you want to die so badly. So maybe that's precisely what you deserve."