A student of mine is a lapsed vegetarian–with vegetarian parents. They object, for religious and ethical reasons, to his meat eating. He retorts with the following argument:
If it’s wrong to eat animals because they’re living creatures, it’s wrong to eat plants, because they’re also living creatures.
My student acknowledges that this is a weak argument but nonetheless reports that this is a successful rejoinder to the extent that his parents do not reply. Let’s say for the sake of argument that this is the case. Let’s further say, again for the sake of argument, that the parents’ argument is both weak in itself and weakly held by them.
This means that his parents do not have (or do not share) very good reasons for their vegetarianism. So, the student replies to a weak argument with an equally weak argument. When I raised this point, he shrugged his shoulders and said: “what does it matter? It does the job.”
Students of argumentation, in my limited experience, tend to study either bad arguments or bad replies, but not both together. And in this case, the bad reply is offered on purpose, because a better reply isn’t necessary.
I’m inclined to think this is wrong, and that the student owes the parents (and himself) a better reply to a better argument. I say this because he’s aware of how bad his own argument is. On the other hand, his parents haven’t offered a very good defense, and answering a better argument would be iron manning them.