In fact, the Xmas scolds are ignorant.
The "X" in "Xmas" isn't the letter "x" (eks) of the Roman alphabet. It is the letter of the Greek alphabet that has the same shape, the letter "chi" (kai). Any word in the English language that has a "ch" pronounced like "k" comes from a Greek word. Where we see "ch" but say "k"--chromosome, character, chiropractor, bronchial--the Greek word would have the single letter "chi." Which, yes, is formed by two crossed diagonal lines.
One of those "chi" words in Greek was "christos," which was translated with the Hebrew word "messiah," but which the Romanized western world at the same time kept pretty much intact, albeit in a different alphabet, as the name-tagging honorific of Jesus. (I wonder if Greeks wonder why we need two letters when one works just fine for them?)
The shape of "chi" was also recognized in the early Christian world as a type of cross, the type that we call the cross of St. Andrew (it's the x shape on the national flag of Scotland, the Union Jack, and the Confederate battle flag). To early Christians, this doubleness of "chi" as both cross and first letter in "Christ" proved to be a powerful sort of pun, and early on the letter had an apotheosis of sorts, attaining spiritual status as a monogram for all things Christian.
No less than John Wycliffe, widely believed to have been the first to translate the New Testament into English, acknowledged the equivalency, explaining in a sermon in 1380 that "X bitokeneth Christ."
Complaining about "Xmas" is like complaining about "WWJD" because it has the letter "J" instead of the name "Jesus," spelled out. Hmm, now here's a thought: WWXD.
So by all means celebrate Xmas! And invite the scolds to go share their spite cake with Ebenezer Scrooge.