People made this exact same "no evidence" argument about animals for years, and many still believe it. The fact is we don't know enough about how plants or animals experience life to be sure of anything.
People would still adopt a plant-based diet because there is no other alternative right now. Purely lab-synthesized food that does not involve cultivation of any other organization is still a long way off from reaching any kind of scale for mass consumption.
I don't disagree, but I don't see how that's relevant to my point.