Well, Christmas is a holiday that has already been largely secularized and commercialized. It's a celebration that Christian groups have already long accepted and shared with the masses. The same is true of Easter and a few other of its holidays. Your family's experience seems fairly different from what I've encountered in the past, but in general Christianity gets a bye because it holds a position of power in the western world and it has encouraged its own spread into as many cultures around the world as possible.

I think a better comparison would be if people were to take up the ritual of prayer of Islam (Salāt) as a way to inject a time of meditation and spirituality into their day. It wouldn't harm anyone, but it would be a turn-off to other Muslim people who see the ritual as belonging to their culture and having meaning there. If Americans were engage in this hypothetical act, chances are much of the meaning to that act would be diluted and/or misinterpreted.

And as I said:

When local: stupid and alienating. When widespread: dehumanizing and, fuck-it, I'll use the word: oppressive.

It's when these practices become engrained in a group of people or in institutions that they become acceptable as a way to re-tell the story of another culture. How many Americans have you met that have proclaimed that Buddhists are peaceful and happy?