Plants are not conscious and do not feel pain. But even if your argument is in good faith and you genuinely believe that the plight of plants is equivalent to the suffering of animals, then that is still an argument for veganism, as producing a kilo of animal flesh requires several kilos of plant matter, thus increasing the total amount of suffering relative to simply eating plants directly.
Humans are animals. Humans do not feel pain differently from other animals. Humans do not suffer differently from other animals. This is why intentionally causing animals like cats and dogs to suffer is illegal and viewed as abhorrent. The only reason this is not extended to other animals like cows and pigs is convenience.
The vast majority of animals raised to be killed and eaten are fowls, pigs, cattle, sheep, and goats. No, humans do not feel pain differently than these animals any more than they feel pain differently from cats or dogs.
Sorry for being rude. No, my [non-]argument wasn't in good faith - it was in response to a parody comment, after all.
But you seem serious this time. The problem with that line of reasoning is: sure, you can (quite literally) weigh the pros and cons of veganism like you did. But why stop there? To sustain a kilo of human flesh you still need several thousands of kilos of plant matter. The ultra-utilitarian solution surely must be getting rid of human flesh? Now I'm not so sure your previous comment was really a parody.
Given that plants aren't conscious and do not feel pain, any line of reasoning that is predicated on the assumption that plants are conscious and feel pain is irrelevant.
Your argument is just antinatalism, but for farm animals. Every animal will suffer in its life. Eradicating an entire population to reduce suffering is pretty extreme. Other arguments for veganism, like the environmental one, are much more palatable.
