Your claim of lobsters not being able to feel pain is wishy-washy because it's a convenient assumption based off of an oversimplification. "Invertebrates don't feel pain because they lack the specific machinery mammals use to experience pain". If you just stop there then yes, it does seem silly to worry about a thing that doesn't exist. However, what I've seen of the models suggests that we are far away from being able to confidently say we have a complete model of a lobster's nervous system.
We can’t yet even define consciousness so of course we don’t have a “good” model. But using our current understanding of the “machinery” makes more sense to me than basing the decision on whatever it is you’re vaguely referring to, otherwise I don’t see what stops one from going to full Jainism. If our understanding of that machinery changes so will my opinion.
You haven't really given much rationale beyond "they seem to react to stimuli". At best, your position that they have consciousness or feel pain analogous to humans appears based on intuition; at worst, on dogma. Neither is a particularly reasoned stance.
No, I've already stated that is a completely reasonable position. It was the main reason behind my decision to become vegetarian. I don't think it's no cost to everybody though and some people's health deteriorates, particularly on vegan diets. However, being conservative in the face of uncertainty is a different stance than claiming they experiencing pain. It also doesn't address how you avoid the slippery-slope argument. For example, we haven't proved plants are not conscious so how do you reconcile a vegetarian/vegan diet with that? For me, that's why I rely on the biological argument that started this discussion. I have a feeling many people just resort to their intuition. Meaning it's just the same position of convenience you railed against masquerading as principled, reasoned stance.
My personal choices aside, there are also reasonable arguments against it that I don't think we should immediately dismiss with hand-wavy anthropomorphic arguments.
