Is there a reason that American Jews should not celebrate Halloween?
"[..] There is a clear historical relationship between the Celtic concepts of resurrection, Roman Catholic responses to it, and the modern American holiday of Halloween.
Thus, Halloween, unlike Thanksgiving, plainly has in its origins religious beliefs that are foreign to Judaism, and whose beliefs are prohibited to us as Jews." ("Collecting Candy on Halloween: Harmless Pastime or Halakhic Prohibition?", MyJewishLearning.com)
"On Halloween people take -- in fact demand -- sweets from strangers. This alone is certainly not a good thing to be teaching children, not to mention that Judaism forbids such a practice. It is also considered terrible behavior." ("Jewish Halloween?", BeingJewish.com)
"Many people compare Halloween and Purim. Besides the masquerading in costume, they are as different as can be! What happens on Halloween? Children go from door to door, saying, "Trick or treat!" Where did that expression come from? The origin is a threat: "If you don''t give us a treat, we''ll give you a trick!" On Purim, instead of going around demanding presents, the children go around delivering presents! What a difference!" ("The Purim Celebration")