Asklemmy

It's not necessarily a fallacy, because the argument that Y and Z are equivalent or sufficiently similar to both justify X is a valid argument.

The argument that they're similar might be an example of a false equivalency however, which is an informal fallacy, and so depends on the circumstances of the argument, since it's not de facto invalid to draw an equivalence between two things.

A simple fine is a just punishment for littering. Someone threw a bag of trash out of their car on the highway (illegal dumping, not littering). Because a fine is justified for littering, and illegal dumping is similar to littering, a fine is justified for illegal dumping.

The equivalence between littering and dumping isn't unreasonable.

A simple fine is a just punishment for littering. Someone burnt down an orphanage (arson and heinous murder, not littering). Because a fine is justified for littering, and arson and murder are also crimes, a fine is justified for them as well.

The equivalence between littering and murder is weak at best, and most would find it unconvincing that we should treat them the same.

(There's a fun related problem where the equivalence is bad, but both conclusions are actually agreeable. It can lead to some weird arguments. "Hitler deserved to be removed from power. Hitler was a man. Stalin was also a man, and therefore deserved to be removed from power")

sounds like a kind of false equivalence to me

I'd say it's a non sequitur

I’d say it’s just a specific case of a strawman argument, but maybe I’m misunderstanding.

The "if my grandma had wheels, she would have been a bicycle" fallacy.

https://youtu.be/A-RfHC91Ewc

Whata you say make-a no sense! False equivalence

I'd say there are two cases:

1. The argument is that Y and Z are similar enough to extend Y => X to Z => X. This might be valid if Y and Z are indeed the same in all aspects that matter, if not then I'd say it's a False equivalence.

2. It is not known whether Z is actually Y or not, but it's assumed to be true to extend Y => X to Z => X. In that case it should be Appeal to probably.

Maybe you have Chutzpah on your mind?

"a man who, having killed his mother and father, throws himself on the mercy of the court because he is an orphan" (Wikipedia)

That's not a fallacy. Their's is an argument by analogy, where Y and Z case are analogous, perceived to have similar characteristics.

Your objection is that the two situations are not similar in some relevant way (need for self-defense, survival situation).

Looks like faulty generalization followed by application of its result to another specific case.

It might be similar to a Motte and Bailey Fallacy. Though that one is more focused on distinct but related definitions than it is for distinct but related situations. Not the exact one that you are looking for, but the related concepts might be a path towards an answer.

https://en.wikipedia.org/wiki/Motte-and-bailey_fallacy

I'm not sure it's a specifically named one, but then again there are dozens, and they're hard to keep straight. In general it is (attempted) rationalization, hand-waving, and kinda... just a bad argument. It does not actually explain why that specific murder was "necessary" - only that it could've been.

The intent is to rationalize, but it might not get close enough to a real argument to pin down to a specific (in)formal fallacy.

Whataboutism?

It’s not a logical fallacy, just a factual error.