If a Moslem sent me a “Happy Ramadan” card, I’d not be offended.
If a Hindu or Buddhist sent me a card to show their celebration of a religious holiday, I’d not be offended.
They want to share their faith with me? Fine. I’ll be happy to share mine with them.
If an atheist were to send me a blank card, I’d be amused, but not offended.
So, ba ba, why the offense?