I couldn't. She killed people, and now that she had a taste for it again, she was going to do it again. And Sam's track record with trusting monsters hadn't ended so well in the past. Add to the fact that he's slowly losing it, and ...

[a beat]

She had a kid.

[another beat]

He's probably going to track me down and kill me if I'm still around in a few years -- I'm giving you fair warning on that one.

[there's a small, dry smirk]

So no getting pissed at me for it.

[he's only half-joking]