I'm not American. And I'm an atheist. Are there actually people who object to "Merry Christmas"? This seems so bizarre to me, I always assumed it wasn't a real thing.
Likely more prevalent are the people who don't like corporations, public services, etc. wishing everyone Merry Christmas year after year while ignoring the holidays of other religions.
To avoid all of this, many places are switching to "Happy Holidays", except there are a not-insignificant number of people who are upset by this and feel that companies/governments should be saying "Merry Christmas" because they should be aligned with Christianity.
As in the OP, there's probably somebody you can point to who holds any dumb position you want to argue against, but there isn't really an anti-Christmas side of the public discourse in America.
I have yet to see anyone get riled up.
What's worse: There are some people who celebrate Christmas but who choose not to wish others a "Merry Christmas" out of fear of offending them. Peak woke.