There is evidence that Christmas originated in the winter solstice festival that most ancient civilizations observed.
There is not any evidence, even a bit, that Christmas originated in the Roman winter solstice festival. In fact, evidence is against the allegation.
In 1-5 AD centuries, Winter Solstice fell on December 19-23, not December 25. See “Winter Solstice 1-500 AD fell on December 19-23, instead of December 25“.
Anti-Christmas groups have been relating those two different separated individual festivals with post hoc ergo propter hoc fallacy1 — because Christmas (December 25) after Winter Solstice (December 19-23), then Christmas caused by Winter Solstice.
Be aware with this fallacy in anti-Christmas argument.
1Post Hoc Ergo Propter Hoc (After this, therefore, because of this) fallacy: A happens after B, therefore B causes A. Example: John sneezed. A minute later, a plane crashed. A plane crashed after John sneezed, therefore, John’ sneeze caused the plane crashed.