That leaves us with a difficult decision – should we continue a practice that was started as a pagan religious ritual? Here are a few things to consider: (A) Does the holiday in any way promote false doctrine or immorality (Galatians 5:19-23)? (B) Can we thank God for what we observe on a holiday (1 Thessalonians 5:16-18)? (C) Will celebrating the holiday detract from your Christian testimony / witness (Philippians 2:15)? This is a decision a Christian family needs to make together. Pray to God, asking Him what He would have you to do (James 1:5).

Balancing the Christian Life
By: Charles C. Ryrie
http://www.christianbook.com/balancing-the-christian-life/charles-ryrie/9780802408877/pd/08777?event=AFF&p=1011693&
References :
TLS

Christians built churches on the pagan sites and adopted their forms of worship in an attempt to get the pagans to become christians.

They then moved Christs birthday to the 25th December and took over Easter to try and take over the pagan festivals and again adopted not just the methods of worship but all the trappings as well such as the tree, holly and ivy, baubles bangles and beads, chickens and eggs!

Christianity is far more pagan than those that call themselves pagan nowadays!
References :

Easter Sunday was celebrated by Sumerians (originally as symbolic of Ishtar, goddess of fertility whose symbol was an egg and a rabbit.) The Christian celebration on Easter Sunday for the Resurrection of Christ was coincidental.
Birthdays? Not sure what you mean. Celebrating the date of someone’s birth is not inherently pagan in origin. It is celebrated throughout the world.
Halloween came from "All Hallows Eve" the predecessor to All Saint’s Day. The date was used due to the celebration of Samhain. Christians, originally, were afraid of this holiday because it revered "monsters." They used the name "Hallows Eve" (Meaning Holy Evening) to combat what they viewed as evil.
Patriotic days are not pagan, nor is honoring your mother.
Valentine’s day was not pagan. It was created by Hallmark (not kidding) to sell more cards during February (their slow time) during the victorian era.
Paganism is an actual belief system, usually tied in some way with worship of the natural world and mysticism. I fail to see how several of the celebrations you listed are considered pagan.

Another question that you might ask is: If Atheists are so anti religion and don’t believe that any religious holidays should be celebrated, does it offend them to get a Christmas bonus? What about time off on "Good Friday?" Do they think it is hypocritical to accept a Christmas bonus if they don’t celebrate Christmas?
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Peopel celebrate Christmas, Easter, Birthdays, Halloween, New Years, Valentine’s Day, Mother’s Day, and Patriotic Days because they get to give and receive gifts, get to party, travel, hang out with friends and family, etc.

Since most people aren’t wealthy, they aren’t able to spend money on gifts, partying, and traveling all year round, so people tend to wait for special occasions to spend their money.

Christians do not worship those holidays.
References :
Agnostic