America is not identified as being any particular religion. We have separation of church and state. Many folks identify themselves as being Christian. However it has no bearing on their secular choices.
Most people "cherry pick" which scriptures or verses they'll follow in their religious dogma. Everyone is a hypocrite about something.
Halloween, Valentine's, St. Patrick's Day, New Year's Eve and Cinco De Mayo are all holidays celebrated in the U.S. primarily for the FUN of it! Some religions are against celebrating birthdays!
No one is being "forced" to indulge in Halloween activities.
Even some churches these days host functions for their member's children to celebrate Halloween safely.