The Luke 2 census - did everyone travel? We know from Luke 2 that each person (or, certainly, adult male) was required to register to his own town. We also know that Joseph travelled (with Mary) from Nazareth to Bethlehem so that they could be registered there:


  3 And all the people were going to be registered, each to his own city or town.
  4 And Joseph also went up from Galilee from the town of Nazareth to Judea, to the town of David, which is called Bethlehem, because he was of the house and family of David


--Luke 2:3-4 (AMP), emphasis mine

The common assumption is that everyone had to be at their ancestral home for the census, however the passage doesn't exactly say that. It states that people would be registered to their own city or town - presumably, the city or town they happened to be in at the time of the registration - and that Joseph went to Bethlehem because he was of David's line.

Since genealogy was so important to that culture, could it be that Joseph travelled to Bethlehem of his own volition to emphasise his ancestry on his official registration, as opposed to being required to go there by the authorities? Is there any evidence that people were required to travel to their ancestral homes as opposed to many Jews choosing to do so?

(By "evidence" I don't mean original documentation as that's obviously going to be pretty hard to come by; I'm really wondering if this has been discussed by subject matter experts and what conclusions, if any, have been drawn.)
It is possible that Joseph's home was in Bethlehem and he had only temporarily moved to Nazareth because he was working on a construction project. I don't know of any case where an ancient government required the majority of people to travel a long distance for a census.

If we read Matthew's account of Jesus' birth, we find that Joseph and Mary intended to make Bethlehem their home upon returning from Egypt, but were persuaded that Jesus' life would be endangered if they settled in Archelaus' realm. Nazareth is not mentioned in Matthew until the family "turned aside" to go there in Mat 2:22-23.

Joseph's trade is specified as 'tekton', which has traditionally been translated as 'carpenter', but is a fairly general term for 'builder'. He may have been a construction worker at the time, moving around from place to place to find work. If so, he might have met Mary while he was working on a building project near her home town, Nazareth[1].

Here's a sermon, United Methodist but probably typical of Protestants who study the story closely:

http://www.dodgevilleumc.org/sermons/2011/joseph-of-bethlehem/

"if we do a careful study of these two Gospel accounts, we’ll find that Nazareth was Mary’s hometown … and I’m pretty sure Bethlehem was Joseph’s hometown"

Once Joseph had decided to accept Mary as his wife even though she was pregnant, the most natural thing for him to do would be to take her to Bethlehem, his home town. Doubtless the census encouraged the timing of the trip, as Bethlehem would be the ideal place for Joseph to register, if it was his permanent home. It may or may not have been mandatory for him to go there.

Joseph may indeed have been motivated by desire to register in the town of his ancestors, whether or not it was he thought of it as his hometown at the time. If Joseph's home was in Bethlehem, it may have simplified the registration process also. But even without the census, Joseph had reason to bring his new bride to Bethlehem, and perhaps find work that did not require as much travel.

[1]: Work opportunities