you are not weighing all the checks and balances
plant life and human life live in synergy and are dependent upon each other, we need them to breath they need us for sustainabilty.. the operative word here is NEED
i have the right to kill plants because they are a necessity for nutrition , vitamins and fiber
eating meat isnt a necessity
plants dont need humans, their existence is in no way dependant upon us. plants existed for millions of years without more advanced lifeforms around.
but the argument about not eating meat since its not essential to our life. well i see some merit to that. if we can get by only killing plants without the need for killing other lifeforms then that is better than killing both.
BUT
one could argue that he may choose to eat only animals, and leave plants to live out their lifes.
and why would he be any less right than the man who chooses to eat plants and leave animals alone?