I don't think I disagree. Fighting the hypo is the equivalent of changing the subject. Sometimes, that's a good idea. I certainly endorse dodging loaded questions. Even better is calling people on the loaded question, if you are brave enough and think it will help. (Unfortunately, that's usually a question of relative status, not relative rationality - but trying can still sometimes raise the sanity line).

My point was only that people sometimes get confused about what is and what isn't staying on topic.

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?"

Is there a way to tell the difference between helpful hypotheticals that illustrate confusing topics in stark terms (like Newcomb's Dilemma) and malicious ones that try and frame a political argument for rhetorical purposes (I can think of some examples, I'm sure you can as well, but let's try to avoid particulars)?

Thus, when you find yourself confronted with a hypothetical based on an incoherent ontology, corrupt definitions, or other examples of confused or dishonest thinking often the only viable response is to challenge the validity of the hypothetical itself.

I generally just ironman their flawed hypothetical and carry on. Sometimes it turns out that the flaws are easily fixed and doing so does not invalidate their original point.