That is an excellent question. As a multi-decade vegan I will respond this way: I don’t know that plants don’t “feel” pain. As a matter of fact, there are some indications that plant do demonstrate a response to what could be considered painful stimuli (see Can Plants Feel Pain?).

The question, IMHO, opinion becomes, what makes eating plants kinder than eating animals? To which I can respond that by all clear evidence animals suffer to a greater degree than do plants. Animals demonstrate a strong preference to avoiding pain in the form of stress and avoidance behavior.

I can see a cow, or a pig, or a chicken respond to a threat and that response is one of avoidance. As a fellow being I can discern that animals suffer when utilized as a commodity.

Bottomline, science has not revealed to us what, if anything, plants “feel”. At the same time, it takes no scientific analysis to discern that animals DO NOT want to be eaten.  The key question is what can I do to be Kinder to the beings with which I share the planet?  Until there is evidence to the contrary, enjoying a vegan diet is one of the easiest responses to that question.

I hope that response is helpful to your mission to understand.

Peace Always, Jim

The above question and answer was originally posted at https://www.quora.com/Vegans-dont-eat-meat-because-of-the-animals-but-how-do-they-know-plants-dont-feel-pain