The question is too general. For example, In the making of a wool sweater, The sheep are not harmed. It fact it is beneficial to shear a sheep. It would be cruel not to do so. On the other hand, To slaughter an animal just for it's skin would appear to be wrong. To use the leather from cattle seems proper, Since the cow is already being killed for meat. The leather is a by product put to good use.
If an animal wants to wear my skin or my dead carcass after I die then go ahead I do not care. The material on these clothes are not alive. Most of the time these materials are by product of animals killed for meat, Why would you argue to waste these materials of animals who are already dead? The job is already done and you can't bring back your little animal friends