I do not believe that Jesus has anything to do with "Christmas", which is a pagan festival related to the Winter Solstice:
In a way, it is more appropriate for this "snaketivity scene" to be present in MI than the more traditional (but mostly fictional) Christmas nativity scene. Jesus came into this world to bring us the truth. Anything which detracts from His authenticity (including the way we celebrate "Christmas") cheapens His gospel.
To the Detroit chapter of the Satanic Temple, I say this: Your statement "the greatest gift is knowledge" is quite misleading. Perhaps you should actually read the Bible before you criticize it:
And out of the ground made the Lord God to grow every tree that is pleasant to the sight, and good for food; the tree of life also in the midst of the garden, and the tree of knowledge of good and evil.
Genesis 2:9 KJV
It's not the "tree of knowledge" ... it's the "tree of knowledge of good and evil". It has nothing to do with knowledge per se, but everything to do with rebelling against and challenging G-d.
If Satan's greatest "gift" to you is something which makes you an enemy of G-d, what kind of gift is that?