What's wrong with "Merry Christmas"?

[dumbledore11214]

Carol responds:
<SNIP>
Question for Alla: I thought that Rosh Hahanah was the day of
Atonement. Is it proper to wish someone joy on that day? It seems
rather like wishing someone "Happy Lent" or "Happy Good Friday." (Not
that I would take offense at such a greeting. I would just consider it
odd.)
<SNIP>

Alla:

Yom Kippur is day of the atonement, which supposed to come close 
enough after Rosh Hashanah.