There isn't one correct answer for people to know. That's your interpretation and most people don't agree with you. Most people would say that dressing up as a vampire is not an unholy act because vampires are not real. Even most children realize they are dressing up as factional characters on Halloween, so it's essentially a horror themed costume party. Most people, even if they are religious, see it as that. Sure, the pagan origin of the holiday is clear, but we can say the same for most of the Christmas traditions, but people still enjoy them and it doesn't make them pagan. People care neither about the origin, nor about the meaning someone else might see in a holiday. They care about what meaning or value they see in a holiday and sometimes the fact that it's fun is enough.
So don't try to read into things that aren't there and join the party ;)