To all people who who are proclaiming that they are grateful that they can again say “Merry Christmas” at this time of year, I ask, “Who ever told you that you can’t?”
The fact that many individuals, businesses and government institutions choose to greet people with “Happy Holidays” instead, doesn’t diminish the expression of your faith in the least.
“Happy Holidays” is meant to be an attempt to include all people in the festivities regardless of their religion or beliefs. Rather than unintentionally exclude people by assuming that they are Christian, we wish them “Happy Holidays” to wish them happiness regardless of their beliefs.
If you want to say “Merry Christmas”, then by all means, do so. Just remember that the person to whom you send this greeting, may not share your beliefs. They probably won’t be offended as they will just attribute it to just another person making assumptions.
If, on the other hand, you’d like to indicate to people that you care about them no matter what their beliefs are, then consider using “Happy Holidays” instead.