"The concept, as dramatized in Christian custom, is quite simple: On October 31, the demonic realm tries one last time to achieve victory, but is banished by the joy of the Kingdom.
The festival reminds us that though Jesus has finished His work, we have not finished ours. He has struck the decisive blow, but we have the privilege of working in the mopping up operation." -Internet MonkDressing up as ghosts, demons, and even satan is a MOCKERY of Satan because Jesus is victorious. The fact that we can dress our children this way shows our supreme confidence in the utter defeat of Satan by Jesus Christ – we have NO FEAR!
For a Christian to not celebrate Halloween because they think it is evil and are afraid of Satan is the same as not celebrating Christmas because Santa Claus and Rudolph aren't real.
Our culture has distorted the celebration to be sure, in the same way it distorts Christmas and Easter. That doesn't mean we abandon Christmas. No, we define it and celebrate it on our terms. Halloween has very rich Christians roots, and it has a lot of potential to be redeemed and celebrated by Christians for God's glory, not shunned or feared.