We each perceive music and create it in a different (if only slightly different) way. The patchwork of ideas that we bring together in our music is like the mixture of genes that form a new person. All of our genetic features are nothing new on their own. It is in one person that they are combined in such a way as to be a new person with their own personality. Just because so much has been done before, doesn't mean we can't produce something new and meaningful with the bits and pieces that we borrow from others. Of course there are some people that are incredibly similar to the point that you might say they are pretty much the same. The same is true of composers. But since when did we start saying that two people being alike is a waste? Why should we say that? If you were born looking just like your grandmother, then you should be proud to carry her memory on your face alongside your own personhood. Same thing with composing. You may compose music that is like something already being made or having been made, but that doesn't mean you should stop. To compose in whatever style is to carry on the tradition of human self-expression in your life, regardless of who may be listening. We compose because it is a part of our identity and it is how we take part in passing on human tradition. At the very least, every composer should be able to share their music with their friends and family. In that way, you enrich their lives (hopefully) and enrich your own. This, at least, is how I look at it. This is how I justify my compositions and to share it with others is the only thing I desire for my music.