I think you make a good point, although there may not be any thing wrong in dressing up like a spook or bunny or etc it is all designed to get peoples attention on any thing but the truth.
To lure kids to the church through false means is Satanic and they are better off to stay away from a false doctrine or belief.
Whose doing that by having a trunk or treat? It's essentially a Christian alternative to Halloween where churches reach kids in a community with the gospel and an opportunity to go to church.
Those Christians are smarter than the ones making Christian kids feel like they are missing out.
But, I don't particular care if a kid goes out trick or treating on Halloween. It had no negative impact on me. My parents were Christians and weren't celebrating anything evil. To deny me the opportunity to do that is what potentially would have harmed me. It would have left the impression that Christianity is so legalistic that it stifled all the fun out of life. Legalism (adding to God's laws) drives people away from the Christ.