There's little darker and more menacing than the cross itself.
Consider: crucifixion was the way the Romans tortured and executed dissidents, rebels, slaves, etc. It wasn't just about torturing and killing a person in a brutal way, people were crucified in very public places, along busy roads. It was particularly common in the outer edges of the Roman empire in conquered territories. It was a statement, "We're in charge, remember that" It was about keeping people in line with fear.
The cross was an ugly, grotesque symbol of Roman oppression.
But because of One who was nailed to a cross, the cross is for us the symbol of victory over death, the symbol of God's defiance against the violent and hostile powers of this world. We proudly wear the cross and display it because by it God conquered the world.
There are other things to consider as well. Why should we be terrified of symbols of death--skulls etc? Death is defeated under the heel of Christ the Lord; and indeed it is our solemn hope that on the Last Day when the Lord comes we shall be raised up from the dead to new and bodily life.
When we take symbols of spooky and dark things, of death and dreary things and transform them into harmless fun and mock them we are declaring that they are not a power over us to be feared.
Lastly, we need to remember what Hallowe'en actually is. It is actually the Eve of All Hallows or All Saints. A day on the Christian calendar set aside for remembering the dearly departed saints of God, to remember that there is no death in Jesus, that death is defeated, and even those who have died live with Him and that one day there will be a resurrection from the dead, there will be a day when we are all reunited again when God makes all things new at the coming of the Lord in glory.
So Hallowe'en for what it actually is is a deliberately Christian day.
The spooky silly stuff is for the kids. But even in that we can use to remember that none of the dark things of this fallen and present age has victory over us, for we belong to Christ who has overcome all the wicked and violent and dark powers of this world by His cross and empty tomb. We have no reason to fear, but we have every reason to rejoice.
"Christ is risen from the dead,
trampling down death by death,
and to those in the tombs,
bestowing life."
-CryptoLutheran
