The scenario I've just outlined is large and complicated, but the evidence warrants a large and complicated explanation. It's not the sort of situation the early Christians are likely to have made up if they were free to have made up whatever they wanted. When the pregnancy is premarital, Mary lives in Nazareth rather than Bethlehem, Joseph is in Nazareth shortly before the wedding in spite of having a home in Bethlehem, etc., the early Christians probably were operating under significant historical constraints that prevented them from giving an account that was as simple and easy as they would have preferred.
See here for an acknowledgment of the significance of one of my points about Nazareth from Christopher Hitchens. Bart Ehrman has gone as far as to refer to Jesus' upbringing in Nazareth as "certain": "Little can be known about Jesus' early life, but one thing that can be said for certain is that he was raised in Nazareth, the home village of Joseph and Mary." (The New Testament [New York, New York: Oxford University Press, 2012], 269)