[marcv81]

"That again, they respond to stimuli but don't feel pain like an animal."

I don't feel this is a valid argument. We only really know how pain feels to us, but we can guess it also applies to other humans, animals, etc. That we cannot imagine how it feels to respond to negative stimuli as a plant should not invalidate the possibility that it is unpleasant.

[chimprich]

It seems vanishingly unlikely that a plant could experience pain. To the best of our knowledge, you need a brain of some sort to experience anything. Even that may not be sufficient: an unconscious human doesn't appear to experience pain.

You could argue that plants may have some unknown structure that allows them to experience pain or other phenomena, but that's no very useful. You could argue the same about rocks. It's impossible to prove a negative.

[abdullahkhalids]

A robot can be designed to respond to stimuli. For instance, an advanced robotic vacuum cleaner moves away when it hits an object that was not supposed to be there, or move away from a source of heat or from water. In what sense are these responses different from the response of a plant or an insect?