It has been a growing trend for several years for certain groups of Christians to refuse to celebrate holidays like Christmas or Easter because they believe those days have pagan roots.
I think it's misguided to think the actions of some group of pagans in the past has corrupted a day God made for all eternity such that Christians can never celebrate anything on that day for fear of inadvertently celebrating something pagan. The same thing goes for inherently harmless activities like decorating a tree or having a game to find hidden eggs. The fact that these things might once have had a connection to some sort of pagan activity doesn't mean that people today have any sort of evil in their hearts or are worshiping a false god in doing them.
So, yes, it's somewhat true that many Christian holidays and traditions had some sort of pagan association at one time (though not all the rumors about this are true). That's not a problem. Christians went into new cultures and used their existing traditions to tell the Christian message instead of a pagan one. They redeemed days of celebration, as they redeemed the people, by converting them to worship the one true God.
Something similar was done by John and Charles Wesley when they took bar songs and used the tunes for hymns. The people were familiar with the tune, but now the song taught them about God and encouraged them to worship Him. Christians changing traditions of a pagan people to instead celebrate and teach about Christ is a good thing. A former pagan association to a day or activity doesn't contaminate the hearts of those who are actually worshiping and celebrating Christ.
Of course, if someone's conscience prevents them from celebrating Christmas or Easter because they believe it is wrong, then they should not violate their conscience. However, they can inform their conscience if they choose to. We are free in Christ and do not have to be bound by ideas of spiritual contamination by association. To the pure, all things are pure.
Christ came to earth as one of us and died in our place so that we can be reconciled to God. That's something worth celebrating. If that's what is in our hearts at Christmas or Easter or other holidays, then that's what we're celebrating, and no other tradition that may or may not have ever occurred on that day can corrupt it for us.