(UPDATE: Greg has a post on personhood up, here).
Margaret Sommerville has an article arguing against personhood for animals. The article is at least 98% bunk (even her attacks against Singer are off base). Except for the honest argument that personhood for animals should be opposed because it destroys human exceptionalism. That's the problem sometimes, what I want is often exactly the opposite of what someone else wants. It's not a misunderstanding that can just be clarified. Anymore than someone saying their opposition of extending personhood to african-americans in the times of slavery was a problem because it destroyed white exceptionalism. No duh, that's a benefit, not a bug.
This article comes by way of A Thinking Reed, where Lee has two posts up responding, here and here. You might also want to check out his post on corporate personhood.
Meanwhile, it seems there is a movement to create an amendment in order to define citizenship as belonging just to humans, and specifically trying to stop citizenship rights to be conferred on corporations. I learn this by way of Animal Rights & Anti-Oppression. Over there Mary Martin makes the argument that corporate personhood is bad for the personhood of non-human animals. No doubt.
Of course the whole thing seems to be caught in some sort of weird double bind. People want to pass this amendment because they feel the recent SCOTUS decision gives too much power over the political process to corporations. If this is correct, passing an amendment, the hardest political thing you can probably do, should be easily stopped by the corporations. Oh well. If the language gets changed to something less anthropocentric, let me know.
There is probably more I want to say on all these issues, and I might get to them later.