Vedic Restrictions: Using animal products

                                                                  Q. I have been reading your questions and answers and enjoyed it very much. My 26 years old son posed this question to me and I find it hard to give him a good, full-proof answer. He concludes that all my answers point to having faith and are not logical or reasonable. Please give me the answer for this question below.
                                                                   
                                                                  We always say that we must be vegetarian and must not kill animals, but how can we justify using animal skin (leather) for belts, bags, shoes and drums used in the temples. Why should we continue using these products that is derived from animals that must have been killed for this? Although we did not kill it, we condone it by using these products.