As we learn from the media, we must try always to criticize both sides of an issue equally. Now, this will not be the full parity treatment–I'd have to find a billboard from the Physicians Committee for Responsible Medicine, or New England Anti-Vivisection Society or another Anti-Vivisection organization. And I'm sure there are many fallacies to be identified in all sorts of protest signage as well as other nonsense. But, as always this isn't about scoring points, but understanding how poor reasoning infects our public discourse. So, in that spirit, let's examine a billboard from Vegan advocacy organization Mercy For Animals.
[Source is MFA's blog]
Now, they're a bit more explicit in drawing the practical conclusion compared to the FBR bill-board, which I previously commented on.
C You should choose vegetarianism.
The premise is only a question, but the question presumably is meant to prompt us to conclude that there is no good reason to kill one animal for food while lavishing the other with love. Stated as the premise that they hope you will grant
P1: There is no good reason to eat some animals but treat others like members of the family based simply on species membership.
P2: In the absence of a good reason to eat some animals, we ought not to eat them.
I doubt that we would call this a great argument, but it isn't an awful one (and I'm not certain I have the best reformulation of it here). Presumably carnists will argue that the premises are false, either by arguing that there is a good reason to differentiate between dogs and pigs and thereby justify eating one of them, or deny that a good reason is needed because they're just animals.
But, the important point here is that the billboard itself is of an entirely different logical character than the Foundation for Biomedical Research that we looked at previously. Not all rhetorical questions are logically equivalent.
Here's another MFA bill-board that, it seems to me, is also logically respectable. I'll leave the reconstruction up to you.
Note: I was expecting to find some easy pickings over at PeTA's website, given their reputation for hyperbole and attention-seeking. (http://www.peta.org/mediacenter/ads/outdoor-ads.aspx). Yet, all of the four "Outdoor PSA's" that focus on animals in research labs seem to avoid egregious fallacies like in the FBR billboard. I'll have to dig a little deeper.