I would argue that atheism is not a belief in nothing

Part of the problem with holding criticism of religion as taboo is that a whole lot of religious persecution is committed by believers of one religion against believers of another, with the ones doing the persecuting then going to say that anyone daring to critisize hurtful actions like calling some a "Christ Killer," for example, are infringing upon their religious beliefs. As long as there are relgions (or as often seems to be the case people manipulating the religious texts and believers) that hold followers of other religions are lesser, or morally unworthy and things like that, it will turn into tyrany of the predominant religion with the "us and only us" belief.

There is a definite difference between discussion which unapologetically states that it disagrees with beliefs of a certain/some/all religious faiths and degrading others for holding those beliefs. I think Dawkin was arguing for the first. While most of those who want any -even POLITE - disagreemet of aspects which are part of THEIR PARTICULAR religion to be silenced will be amongst the first to toss out.

Christmas isn't really a Christian festival

The early church frowned upon it and the Puritans repudiated it, since the focus was on Easter (which is what Handel's Messiah actually celebrates). For that matter, the gospels arguably had Jesus being born in spring or early summer (when shepherds watch their flocks by night).

Its celebration in America may be mostly due to the Irish (like other occasions when drinking is customary), though the emblems of the occasion are variously German (the Tree) and Dutch and English (Santa Claus) but the resulting confection is quintessentially American.

Saturnalia isn't the only original root; we northern barbarians didn't stop celebrating the solstice (or the rest of the old holidays, for that matter) just because we were Christianized.