Taking a leaf from a tree is not "hurting", because it'll drop them anyway later. Now, if you take a rope around the trunk of a tree, and don't put something protective between, you'll kill the tree since you'll cut of any flow of minerals, water and sugger between the leafs, and the roots.
A flower is different. Most flowers won't feel much, since they do, as a tree, drop it's stilk (think it's the same as in danish) and the main flower, where as the root is the heart, and as long as you don't do anything to it, a flower can actually live quite a long time, for a plant of cause.
Animals are different from plant in many ways. Where animals can show emotions, mate and be protective, plants can't. They can show illness, and suffering to some degree, but that's it. I think humans don't think so much about plants, because we ofcause see a bigger similarity between ourselfs and other animals.
As with the dinosaurs, they don't see eating plants is wrong, since they can't imagine how it is to be a plant, or a tree.
Besides, there is nothing wrong with eating meat or plants. Either we do it, or the rest of the ecosystem does it.
