Lanny, I address your points:
The Atheist’s Points:
1. Christians use Christmas as justification for....adding paganism to their observance of the “birth of Christ”.

I know of no Christian within my circle of influence who adds...a tree, holly, yule logs or anything else in any sense other than as tradition....with no meaning attached....or they are added with a Christian meaning attached. In any event they are “adiaphorous”. (things indifferent) The main intent of Christians that I know come to Christmas celebrating the birth of their Savior...through family gatherings and exchanging gifts, through worship on either or both Christmas Eve and Christmas day some also observing the Lords Supper.

2. Christmas has been added as a festival among Christians contrary to scripture.

No where in scripture are we commanded to not observe and celebrate the birth of our Savior. Every Sunday for the Christian is such a celebration, for not only the birth but also for the death and resurrection. To observe one day per year in memorial of our Saviors birth does not constitute the addition of an observance contrary to scripture. What you observe in Christians during Christmas is not the requirement of a ridgid unbreakable law...but an observance of a day that has been indelibly etched upon our hearts by our creator Himself.

Jer 31:33 But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.

Christian celebrate Christmas because God has filled our hearts to overflowing with love and gratitude for His salvation towards us. Truly the angelic host said...Peace one earth goodwill toward men. (Luke 2:13-14) Through Christ we are reconciled to God and He has brought to us not judgement...but goodwill and peace with Him...and for this we are eternally grateful and celebrate this Peace on Earth..Goodwill toward us that He has implanted in our hearts and brought to us on that first Christmas Day. This is what we celebrate!
Lu 2:11 For unto you is born this day in the city of David a Saviour, which is Christ the Lord.

Jesus said: “The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.” Mk 1:15

You may be confusing “Wall Streets” observance of Christmas with the real thing. Dig deeper!

Dave