I agree. The animal kingdom, as such, is a completely agnostic in its definition toward sentience. I once asked my cousin, a vegetarian for twenty or so years, whether she had any moral qualms about eating an anemone, for example, a creature that likely can't feel pain in any way that we would describe as pain, given that it lacks the mechanisms to do so from a neurobiological point of view. She told me yes, but couldn't articulate why. Not that her opinion isn't valid, but it perhaps points to a critical lack of knowledge of how organisms interact with their environment, and how pain is processed. In my world view, the grey area is around birds and mammals. That is, I have no objection whatever to boiling a lobster.[W]hen a living thing has a primitive or no nervous system the word "suffering" may not even be meaningful.
I was with you up until your last sentence. My partner identifies as vegan and has done for more than a decade. By way of background, she has a PhD in animal ethics and has worked as an ethicist for research institutions. She and her vegan friends have no problem eating bivalves: mussels, oysters, abalone. There seems to be widespread agreement among vegans that they're about as sentient as a flower. I'm very happy to agree. *Edit: Updated the link because the DFW article is such a good read I decided it deserved its own Hubski entry.
Yes I threw that in to be intentionally provocative. The lobster obviously has a nervous system. It lacks, however, anything like the pain processing and memory mechanisms that mammals and birds possess. I shall respond more fully after reading your link.