You can doubt it because it's too romantically Moses-themed to take seriously...
Or you can doubt it because you don't believe God sends dream-angels...
Or you can doubt it because you want to sit at the cool kids' lunch table...
Or you can simply accept it, and then start doing History based on the Gospel.
Like this:
When Herod died, Joseph rose, and started back with Mary & Jesus towards Judea. But before Joseph could reach Jerusalem for Passover, the holy family got word - most likely from pilgrims fleeing the scene - about the massacre caused by Archelaus, who was acting as King (Matthew 2:22, Ἀρχέλαος βασιλεύει), ruling just like his father Herod had ruled (Josephus' Antiquities 17.189, 194-5, 200-201, 205, 208, 215, 217, 218, 219, 230-233).If that story is reliably true, then 4 BC is the one certain date in Jesus' entire chronology. It could also mean that Matthew 2:22 is a reliable starting point for more such work on Jesus' personal history.
Stay tuned.