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. 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.

In other words, 'don't fight the hypothetical' is generally equivalent to 'let your opponent define the terms of the debate however he pleases' - rarely good advice, especially outside of a classroom setting.