I don’t think it’s intended to be a good faith argument, as you’re probably already aware. I’ve never heard someone actually start presenting evidence that negative tropism and communication alone automatically equate to pain. It’s already a very abstract and subjective phenomenon among people, with factors including, physical, chemical, psychological, and even social stimuli.

I don’t imagine someone being able to effectively compare that to something without nerves. I’ve heard plants have internal chemical signaling systems. So do we, and we don’t feel them until they affect the nervous system, sometimes not even then.