I think animals can suffer. The fact that the animals can't tell us how much they hurt gives us the idea that they don't suffer alot. I also think that humankind wants to conquer earth and all its inhabitants. Killing animals makes us more dominant and puts us at the top where we want to be. I am not saying that killing animals is unreasonable, I am just saying that animals can suffer.
Plants are the same way.
I don't think that in the future there will be a equality between plants, animals, and humankind because we will always need the feeling of being in control of the elements that surround us. We care for plants and animals because we as humans are dominant over these things and it is our duty to take care of these things. Plants and animals are choices that humans can have. A person can decide whether or not to have pets or plants. If we do decide to have either, it is our responsibility to take care of them because if we don't, then they will die.