Is there a fallacy involved here?

I recently got into a discussion with someone about defining veganism and they used a lot of formal logic to show my definition led to absurdities according to them. I had said my minimum definition would be ‘a position against commodifying and exploiting animals’. From this they asked would it be ‘vegan’ then to hunt Wookies (this assumes Wookies wouldn’t fall under ‘animal’) So essentially I could change the definition to ‘sentient beings ‘ in place of ‘animals’ to cover aliens and A.I. etc. I felt this might be some sort of fallacy where just because I’m not covering all eventualities with a minimum definition it is leading to saying things like ‘it would be vegan to…’ which seems absurd. I’m not opposed to expanded or tightening up the definition of needed. Thanks. 

From what you shared, this seems like a useful thought exercise.

Veganism, in my view, includes a cult-like element where activism masquerades as critical thinking. The argument being presented sounds like a reductio, which can be a useful tool. However, some vegans  often abuse logic and reason and focus more on trickery and word games. I found it so fascinating that I wrote an entire book on it where I explore these arguments in great detail.

Forgive me, but I'm a bit confused. It strikes me your response is more of an argument than a classic definition e.g.:

"I had said my minimum definition would be ‘a position against commodifying and exploiting animals’."

Veganism is simply a personal dietary, medicinal, and sartorial regimen that eschews the consumption of animal by-products for food, clothing, and other applications.

There are myriad reasons for this personal choice and not all of them are political, moral, or activist positions. Health, personal preference, culture, and other psychological factors could lead to this decision. 

The diversion to Wookies is just a weak, red herring, ad hoc rescue.  By our own taxonomy, Wookies would most definitely be classified as animals without the superfluous appeal to possible "others".

P) Veganism is defined as a position against commodifying and exploiting animals.

P) X is an animal.

C) It is wrong to commodify and exploit X.

Under your definition, assuming X was, say, a chicken, it would be wrong to commodify or exploit it. But say I introduced something else - Y - which does not count as an animal. It may then be fine to commodify or exploit it.

What happens next depends on what you are trying to argue - if your consideration covers all sentient beings, your definition obviously falls short. However, if you genuinely only wanted to cover animals (and not, say, insects), then there's no problem - and given that wookies are humanoids, they'd probably fall under non-human animals (remember humans are 'animals' too, in a sense, so this isn't weird).

Make sure you double-check premises. It (probably) wouldn't be vegan to hunt down wookies!

In terms of fallacies, if you accept that your previous definition was not sufficient to establish your intended point, there isn't a problem. It's only when people play fast and loose with the meaning of words to hide a misleading argument that it becomes murky water (see definist fallacy and moving the goalposts). Your interlocutor also didn't commit a fallacy; they used a valid technique called reductio ad absurdum.

Maybe logic chopping because maybe animals are usually the subject matter in veganism.