As has been said Christians do celebrate Passover. I had my bris, but was raised more or less a Quaker, married to a Catholic. Etc., etc.

I've attended many seders over the years, A majority were in the Jewish family tradition, but a significant minority were among Christians of various denominations, the most recent Catholic. To my surprise, some of the Christians ones even had their own liturgies, rewritten more or less extensively to accomodate a different theology. My impression was that they werecomfortable with assimilation and syncretism as long as it was others assimilating to them. I don't doubt their sincerity. But it's sort of like the time I attended mass with a small group of Catholics in a hotel bar. The priest, about as liberal as they come, wondered later why I didn't accept communion.   The idea that if he was generous enough to offer communion to a non-Catholic I shoudn't be grateful enough to accept it was something he didn't seem to be able to comprehend.   The same flavor has infused most of the Christian seders I've attended. The ritual has been adapted to Christian theology, with a common assumption that that is a noble concession on their part.

Perhaps I'm being overly sensitive.