But as an Atheist I will say that, while I might or might not celebrate Christmas (which did not originate in Christianity), I would definitely not want to be married in church nor have religious procedure at my funeral. As an Atheist that is not of any interest to me.
Christmas is a holiday derived from the Pagans, which the Romans developed into Saturnalia, a celebration of Saturn on the winter solstice. The Christians later adopted the holiday as their own celebration, possibly for the purpose of converting others. But there's a stronger reason I think the holiday has been adopted by so many and still continues today, because it's simply a fun holiday that brings family together. Because it's not necessary to incorporate Jesus into the holiday (and Santa has taken over for many Christians as well), I see no reason why the holiday should be exclusive to anyone.
As for getting married in a church, I do doubt that most atheists would want to. But some may hold their wedding at a chapel for sentimental reasons, if their family is religious they may want to please their parents and elders by respecting their beliefs.
A funeral is for the living more than the dead. It may bring peace to their religious family members if they could indulge in rituals to comfort themselves. Some people also consider their family's religion, whether they believe in it or not, to be a part of their culture and history, so it could be something incorporated at any family gathering.
For one, people celebrate Christmas for the presents and family not the day Christ was born(also he was born in spring and it wasn't a Christian holiday to begin with)
The person's significant other may want a religious ceremony which might influence where the wedding is held.
Atheists with a religious family might have a religious funeral service in order to help their family move on.
Most people will celebrate Christmas regardless of their beliefs, and it wasn't even Christian to begin with, it was originally Pagan. Plus most atheists were or knew Christians, and most likely celebrated it when they were kids, so obviously they would keep the tradition.
I can't say anything about marrying in a church, but I know a lot of people do, even if they aren't Christian.
Originally the concept of Christmas was a pagan holiday, and christans stole it to make their religion more popular, it's also a holiday that everybody knows, and almost everyone celebrates it, regardless of religion.
Regarding marrying in a church, it doesn't really matter what religion you practice, the most common marriage is the Christian marriage, so most people would marry in a church, as it's the most familiar to them.
As an atheist, I celebrate Christmas because I've been doing it even before I was an atheist, and everyone around me does it, so it makes sense to celebrate it.
Celebrate a religious marriage, nor want to have religious procedure at my funeral - as an Atheist the religious aspect of either is unimportant and insignificant to me - but Christmas is different, as it does not originate in Christianity. Also, Christmas is just a fun holiday, so I think many Atheists still celebrate it.
Because two out of the three are things I don't/won't do.
I celebrate Christmas because I don't really consider it a religious holiday, plenty have already talked about it's Pagan roots so I won't bother getting into that. I hate and love Christmas at the same time. I hate getting gifts, but I love giving gifts.
My first marriage wasn't in a church, and my upcoming marriage won't be in one either. My fiance, being more of a godless heathen than I am, has made sure to keep religion completely out of the ceremony. I imagine other openly admitted atheists like she is would probably do the same.
As far as my funeral, I see no point in it having anything to do with religion, but I won't care anyway, I'll be dead.
Recently, this last year, we did. My son is 4, and since his name is Zoroastrian for "coming of the light" the Deygan festival, I have no issue embracing it.
I was married in a church. The Unitarian church. Unitarians accept atheists, agnostics, and Zoroastrians as a matter of fact.
Therefore they should not perform any thing that is related either directly or indirectly to god. Christmas is related to christian god and his son Jesus. Therefore atheists will not celebrate it.
Marrying in church means you marry in front of god making him an witness to your marriage. It is the same god whom you don't believe. How could you make somebody witness in whose existence you don't believe.
Performing religious ritual in funeral means you are praying for heaven to god. How could you do that when you don't believe in god?
Atheists will not pray to god when the airplane starts falling from sky for the same reason.