I Will Ask You Questions - Now with MORE fantasy ecology!

These are interesting questions, could I have one too?

YOU DON'T GET TO ASK THE QUESTIONS HERE, BUB! Sai does. Sai, give me the question you would have given Coldblooded if he hadn't crossed the line.

Imagine that humans were to encounter a sentient alien race that acquired energy through photosynthesis and considered all plant life sacred. They had since exterminated as much animal life as possible from their planet. They are surprised by the existence of human sentience, since they see animals as strictly parasitic with no need for higher reasoning. You are assigned the task of convincing the plants to treat peacefully with humanity. Assuming no problems in translation, how would you go about arguing for the existence of humanity and animals in general?