'Loki's Wager'

The continuum fallacy occurs when a reasoner claims that the lack of a binary distinction between A and B means no useful distinction exists between the two. A related concept is Loki's Wager, which is the insistence that if a concept cannot be defined, it cannot be discussed.

Brok: I'm here to collect your head.

Loki: Very well, you may take my head. But you may take no part of my neck!

Except 'head' is a difficult term to define, because some parts of it are independent, but other parts connected to the neck. Yet, the dwarves in the story were forbidden from taking any of Loki's neck. Thus, they could not touch him at all.

By appealing to vagueness - the inability to define a term - we can avoid having a conversation entirely.

Here's a possible example:

Murray: People shouldn't make comments that are offensive to minorities. 

Christine: Who gets to define 'offensiveness'? If we cannot agree on what is 'offensive, the topic is irrelevant.

Are you convinced that this is a good example of the fallacy? Discuss.

I can think of an example where this logic happens very regularly. When discussing the topic of morality, it's often argued in one form or another:

if an objective foundation for morality cannot be agreed on, then there is no way we can determine what's right or wrong. People will define right and wrong differently. So morality is not objective.

I think this is sort of like the ambiguity fallacy. The person is making a conclusion ("morality is not objective", "discussing offensiveness is useless") based on the asserted ambiguity of the term. However I think in both cases the conclusion is out of place. Just because not everyone agrees on what's ethical or offensive, it doesn't make asking those questions meaningless. The presence of ambiguity does not mean the inquiry is futile and isn't worth discussing. Its very possible that we just need to do more research into these areas in order for our understanding to improve, and having discussions about it is necessary to improve our understanding.

I like the name appeal to futility for this logic.

*Update* after some discussion, the fallcy that has come up that best describes these arguments is Inflation of conflict

insistence that if a concept cannot be defined, it cannot be discussed.

This makes sense to me in a loose sense—if interlocutors have difference understandings of a concept, they talk past each other. It makes sense to agree of a definition before engaging in a conversation/debate about it:

Murray: People shouldn't make comments that are offensive to minorities. 

Christine: Who gets to define 'offensiveness'? If we cannot agree on what is 'offensive, the topic is irrelevant.

Murray: Your point is well taken. So let's define "offensiveness" for our purposes similar to how the legal system defines "reasonable doubt," Granted, people will disagree, and there will be some grey areas that can go either way, but most importantly, this will help us to avoid those comments that are clearly offensive.

Christine: That makes sense. Perhaps a better rule would be "people should consider how their comments might affect others and consciously use judgement before making them in an attempt to avoid offending others," since we have no control over how other people respond to stimuli.

Murry: That sounds fine to me.