Hypotheticals are a powerful tool for testing intuitions. However, many people believe that it is problematic a hypothetical does not represent a realistic situation. On the contrary, it is only problematic if it is represented as being realistic when it is not realistic. Realism isn’t required if the aim is simply to show that there is *some* situation where the proposed principle breaks. We may still choose to utilise an imperfect principle, but when we know about the potential for breakage, we are much less likely to be tripped up if we find a situation where the principle is invalid.
It is instructive to look at physics. In physics, we model balls by perfect spherical objects. Nobody believes that a perfectly spherical object exists in real life. However, they provide a baseline theory from which further ideas can be explored. Bumps or ellipticity can be added later. Indeed, they probably *should* be added later. Unless a budding physicist can demonstrate their competence with the simple case, they probably should not be trusted with dealing with the much more complicated real world situation.
If you are doubting a hypothetical, then you haven’t accepted the hypothetical. You can doubt that a hypothetical will have any relevance from outside the hypothetical, but once you step inside the hypothetical you cannot doubt the hypothetical or you never stepped inside in the first place.
This topic has been discussed previously on LessWrong, but a single explanation won't prove compelling to everyone, so it is useful to have different explanations that explain the same topic in a different way.
TimS states similar thoughts in Please Don’t Fight the Hypothetical:
Likewise, people who responds to the Trolley problem by saying that they would call the police are not talking about the moral intuitions that the Trolley problem intends to explore. There's nothing wrong with you if those problems are not interesting to you. But fighting the hypothetical by challenging the premises of the scenario is exactly the same as saying, "I don't find this topic interesting for whatever reason, and wish to talk about something I am interested in."
In, The Least Convenient World, Yvain recommends limiting your responses as follows:
[Say] "I completely reject the entire basis of your argument" or "I accept the basis of your argument, but it doesn't apply to the real world because of contingent fact X." If you just say "Yeah, well, contigent fact X!" and walk away, you've left yourself too much wiggle room.
You may also want to check out A note on hypotheticals by PhilGoetz