There is no need for an accusation of illegitimacy. It does not come into it. There is a mistranslation of Isaiah, but this is not all of the story. There are various, including a young woman who gave birth before her first period (because sex started early). It is common to give magical birth origins to figures where divinity or hints of divinity is suspected. It was done to Buddha, for example. But Jesus (nor the Buddha) did not claim divinity, and this only happened in the Christian community later, the one that wrote the texts and did construct the birth narratives using the Hebrew Bible as the guide to how and where the Messianic figure would be born.

The simplest explanation is that no one said and no one knew. Mary is not going to say, hang on how did this happen in public. If she did it would have led to rumour; but none of this is necessary for a rumour that the father was not involved. Once again people want to find history where it is inaccessible, instead of concentrating on what matters which is the writing process in the filter of a claimed resurrection.

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