2) Because it is the same concept as allowing a 1 year old to believe in Santa Clause of the toothfairy. It is called innocence and I believe a child can live within that innocence until they mature out of it assuming it is healthy mentally. If I were to take that further and dress my girlfriend up, then that would make the difference. Also, I completely understand going to an office holiday party as a social gathering. My question was to those who actually do go the whole nine yards in their own homes when no one from the outside is around. That is very confusing to me. If you are an adult and you have the Christmas tree with the star on top, I really have to question why you would avoid acknowledging what that star means.
Also, when I was a kid, my parents even took us trick or treating a few times. We would get the costumes and I even remember my mom carving a pumpkin with us more than once. They also explained to me as a kid what the history of Halloween was about and what they didn't agree with about it. I was never in the dark about why we were allowed to participate...because we were kids. My parents also never allowed us to believe in Santa Clause even as infants. We might throw a plastic Santa outside for a lawn decoration, but my dad even built a nativity scene that we still have today. We weren't allowed to just join into shit without knowing the background, the pros and the cons.