This is blasphemous sacrilege. The Virgin Mary is the Mother of God in Christian teaching, and as such no-one should be permitted to display such a poster

This is a bit tricky. The people displaying it are themselves a Christian Church, so it is not exactly analogous to the Krishna/Buddha examples. I'd certainly be unhappy if it was an advertisement for a pregnancy testing kit, for example, because the reasons you give. But as it is a poster by a Christian Church aimed at getting people to think more about the reality of Christmas (as Christians perceive it), I'm not opposed.

(On the other hand, I am always wary of the phrase 'no-one should be permitted', whatever it applies to.)