Life is also a creation of Allah whether it, be of humans or animals. Some creation are created for other creations, and by the order of Allah a life of a creation becomes food for another creation because of this there is nothing wrong in slaughtering animals. It is the creator of these animals who have allowed us to take away their lives and use their meat as food. Life is created to be wasted, however it is not us who can determine what live to destroy and in what form. It is only the creator who allows us to do that under his guidelines such that we cannot torture the animals etc.
According to the modern science, everything has life in it including the vegetation and grass and also the bacteria are filled with life. Destroying any of these things is also wasting of life or destruction of it. Hence, it is not appropriate to say that taking away life is wrong or to make that a principal. The principal is that if the creator allows us to use something as food this is his right and he can do it.