Sadly, we don't live in a world where all hypotheticals are actually neutral excercises in deductive logic. In real debates it's quite common to see people constructing hypotheticals that implicitly assume their position on some issue is the correct one. If you accept one of these hypotheticals you've already lost the argument, regardless of the actual merits of the case.

I'm not sure exactly what you have in mind, but I think in that situation the best response to be explicit about what's going on.

e.g. "I would definitely choose Option A as I think that generally speaking and all things being equal, it's better not to torture puppy dogs. But so what? What does that have to do with my original point?"