Some people who would be considered non-emergency are needed, like folks at hotels since some of us will need hotel rooms over the holidays, either because there isn't enough room to stay at someone's house or we need our own space for our own sanity.
And a lot of restaurants that are open are owned by people who don't celebrate Christmas. So I don't see why they should be forced to close on a day when they could make considerable money when it doesn't have spiritual significance for them.
But I agree that theme parks and the like don't need to be open. I find the NBA games played and televised on Christmas Day to be somewhat bizarre. The visiting team most likely had to come in the day before and thus, didn't get to spend the day with their families, not to mention all the TV folks - cameramen, producers, announcers, etc. - and all the stadium/arena workers. I know people who go to a movie on Christmas Day. It's a tradition in their family. Again, I just find it strange.
But if the demand is there and people are willing to work, I guess it'll happen. Just don't expect me to be a part of it.