Every November, a predictable article will appear either in a national newspaper, or on a prominent website. In that article, somebody will say that Christmas is being ruined by 'politically correct snowflakes' who don't celebrate the occasion out of fear of offending somebody. The more hysterical opinion pieces will claim that people are trying to get Christmas 'banned.' Nobody's really trying to ban it, but it does seem that millennials genuinely do avoid the phrase 'Merry Christmas.'
A NewsHour poll conducted last Christmas revealed that under-30s are the only age group who are more likely to wish you 'Happy Holidays' than 'Merry Christmas,' and their reason for doing so is that the phrase is more inclusive. That doesn't mean they're 'ruining Christmas' though - over two-thirds of them still put a Christmas tree up every year. They're just choosing to celebrate the event in a more inclusive manner.