To what extent has "accepting everybody" turned into washing out definitions and meanings as well as diversity?

Marriage use to mean man + woman + promise to God. But in order to "accept" everybody the word marriage is no longer allowed to be exclusive to a definition.

Christmas is no longer exclusive in an attempt to "accept" everybody as well.

To what extent does "accepting" ostracize others? Why can't we just make up new words instead of redefining old words? Nobody gets upset that a specific arrangement of candles is called a menorah...why can't it be referred to as Holiday *insert term here*?

World English Dictionary
Christmas (ˈkrɪsməs)

— n
1. a. the annual commemoration by Christians of the birth of Jesus Christ on Dec 25
b. Also called: Christmas Day Dec 25, observed as a day of secular celebrations when gifts and greetings are exchanged
c. ( as modifier ): Christmas celebrations
2. Lady Day Midsummer's Day Compare Michaelmas Also called: Christmas Day (in England, Wales and Ireland) Dec 25, one of the four quarter days
3. Also called: Christmastide the season of Christmas extending from Dec 24 (Christmas Eve) to Jan 6 (the festival of the Epiphany or Twelfth Night)

[Old English Crīstes mæsse Mass of Christ ]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin & History

Christmas
late O.E. Cristes mæsse, from Christ (but retaining the original vowel sound) + mass. Written as one word from mid-14c. Father Christmas first attested in a carol attributed to Richard Smart, Rector of Plymtree (Devon) from 1435-77. Christmas

If I didn't believe in God but the culture I was part of had been celebrating this day for so long, I wouldn't be offended that it was referenced as Christmas vs. Holiday.