The skull represents our (your) ancestors that have gone before us. It’s about honoring our past because they are, after all, who we owe our very lives to… no matter how screwed up they might have been. Its not worship of the dead, but honoring their lives in the same way that we honor the lives of those people we know who are alive, messed up, but family. The skull is a symbol, much like anything else in spirituality. Nothing evil, just a symbol for our past.