Well, plants have no feelings or nervous system. It isn't very different for them to be alive or dead as they can't suffer. Also, again we need to eat to survive, it's not something we can stop. However, even if I think this way, two years ago I found that in the park where I usually walked with my dog, the biggest tree had been cut. I can't explain why, but I felt kind of sad.
A) I'll eat plant or animal.
B) I rarely do the killing myself, including plants.
C) From philosophical perspective, it doesn't matter (to me) if suffering is involved or not. And to whatever degree it might be, I'm sure we humans can think of ways to minimize that. Make it a swift death.
D) You seem to mostly agree with where I'm coming from. I think it depends on the animal / organism as to how much we care whether it is to serve human needs or is something that deserves own rights.
On a related note, it is still weird to me how bugs (mosquitoes) are one of the only animals I can think of that can eat us in front of us, and we generally don't do much about it. If rabbits gnawed on us, in front of us, I don't think you'd see a rabbit anywhere within a 10 miles radius of where humans congregate. But bugs we let do just this. Sometimes I really think we are serving them. Seriously.