Anyway, you're going to have a problem proving that plants feel pain since they lack all of the elements that cause the experience of pain in animals, such as nerves and brains.

colanderman was that you had to prove they don't before eating them, so I pointed out that until recently, we didn't even know of such elements.

I claimed that if you make a distinction in your morality between animals and plants based on their ability to feel pain, you have that duty. (Note that this is a claim about the consistency of a morality, not about one particular moral system.)

If on the other hand your morality does predicate your moral right to eat something based on its ability to feel pain (as our ancestors did), then there is no such duty.

(Of course there is also a grey area between these -- a morality based on a creature's ability to express an experience of pain is more broadly accessible.)

(i.e. My comment is a critique of the consistency of the moral system the GP set up; it is not an absolute moral judgement.)

Instead of defending our current habits with theoreticals, shouldn't we determine our actions based on the information we have available to us, with respect to the alternatives?

Personally, I take the position that everything I do probably has a negative impact somewhere. Taking the car, bus, train, or staying at home all have consequences for the environment. While I don't lock myself in my apartment, I do regularly review my lifestyle choices and see if they align with my values.

The same is true of the food I eat, both from an environmental point of view as well as how much suffering is involved.