It's all to do with control. Where does it say in the Bible you can't celebrate your childs birthday? Where does it say you cannot grow a beard and be successful in your Christianity?
They control every part of your life - the way you worship, when, where, how, your view of God and what you think he wants, it effects your work, your family, both intimate and extended, your rituals (praying before meals etc), how you spend your free time, what and when you celebrate, how you sleep with your partner - even whether your shave or not or how long your hair is!
They manipulate all of it using misapplied scriptures and the moral judgement of the self appointed as justification.
You will not get an definite yes or no to the thanksgiving issue. It's a 'conscience' issue - in other words you are supposed to police yourself. If you have any doubt it's wrong, you're conscience should say don't do it!! It's all part of the manipulation.
You're conscience is slipping defd, using Satans tool, the internet, to look for spiritual guidance is a Jehovah no-no.
Chuckler