As best we can tell, they want to keep being alive

Not necessarily, they want to spread they're seed. Cereal grains will go into senescence at the end of the season, basically accepting it's going to die and putting all of its energy into its seed so it can come back next season. Like a fruit at that point the grain "wants" to be harvested and spread. They don't really care if they survive another week before winter sets in, they care about there seeds having everything they need for the next season, which humans provide.

To make the case that plant farming is unethical you'd have to prove the plant doesn't want to live on a farm. That's pretty easy with animals, open the cage and see if they leave, but plants can't do that. Up until that point of harvest though the plant is probably living an optimal life, free from pests and competition from other plants so I'd guess it would choose the well manicured field over the wild.

First: Everyone already knows that there’s no way to consume anything without causing harm to something else. It’s why the definition of veganism includes the phrase “as much as possible” not “entirely”

Second: even if we considered a plant’s life as equally valuable as a pig/chicken/cow’s— eating a vegan diet STILL causes less suffering. When you stop eating animals, you can stop murdering all the plants needed to feed those animals.

So the argument of “what if plants suffer?!?” Is bullshit, and already solved by veganism.

The other user’s thought experiment about lab grown meat is more interesting, but it’s not reality yet, and you’d need to understand the specific process for growing said meat to accurately estimate the potential avenues of suffering.

More or less. I'm not trying to debate why eating plants is better than eating animals, it's about specifically the conflation of leftism with veganism. A leftist's opinions of solidarity can apply to humans alone, allowing exploitation of animals. It can apply to animals but not plants, as would most vegans. It can apply to plants and all living things as well, in an effort to minimize the ecological impact of all human behaviour including agricultural impacts of harvesting plants and animals, as some environmentalists would (an example is the degrowth movement to show these aren't imaginary arguments), and so I offered what could be a more positive alternative. Leftism is inclusive of all these things both broader and narrower than veganism. So my core argument is specifically that equating the two, as OP's title and image has, is wrong. I think I'd agree with most that eating plants is more moral than eating animals, but to reiterate, I'm not trying to debate what constitutes sufficiently moral consumption, because I believe that varies based on each person's judgement.