The line is sentience. If they can experience their surroundings. Bacteria don't feel pain or care about "Meeting their doom", they are machines.
Also animals in the field can run to the edge when they hear the combine coming... theyre not just gunna sit there and die: https://www.surgeactivism.org/articles/debunked-do-vegans-kill-more-animals-through-crop-deaths
Even if harvesting plants causes a bunch of animal deaths, it would still be more ethical just to eat the plants rather than feeding them to a cow or chicken to then eat.
The answers to your propositions are quite simple, you just choose to not see them or ignore them because you prefer your tastebuds over anything else. Other sentient beings, the world, us...