I agree that some Christians are quite inclusive, and are not pushing their religion so much as just wishing everybody to have a good time during a holiday. I have an extremely close friend who is very devoutly Christian, but also an extremely nice, very intelligent guy who would not push his religion on anyone or hold it against them if they believe differently.
But not all. I know (and worked with) people who if you responded to them saying "Merry Christmas" by saying "Happy Holiday" they would be miffed, would think that you were trying to "rob Christmas of it's meaning", and would keep a grudge against you for that.
In other words, some Christians still believe very strongly that the default behavior should always be Christian oriented because the USA was "founded as a Christian nation". If you're not Christian, well you can suck it up because "we can't oblige every little belief", and "it's just secular ceremonialism".
And that type of thinking goes on year round, not just at holidays. These Christians think everyone should go along with the Christian way of doing things just because. They are, knowingly or not, giving the finger to non-Christians all the time. Giving them a knowing finger back may make some pause and think why.