Most of us use census data in our research without giving a thought to why it was gathered. Anyone curious about the United States' decennial census quickly learns that a census is mandated every ten years by our constitution, for the purpose of apportioning seats in the House of Representatives. No ethical issues there, so long as you ignore the apportionment calculations that undervalued non-white persons.
Other censuses require a second look. The United States gathered information on Native Americans throughout the 19th century. This information was ultimately used to displace Indian populations. The 1940 census was misused—against the wishes of the Census Bureau—to track down and detain Japanese-Americans after Pearl Harbor.
The most egregious examples of census-abuse come from Nazi Germany. Special censuses and registrations of Jews and other minorities were conducted in Germany and occupied nations for the purpose of expediting Hitler's "Final Solution." The ethnicity of their victims was established, the demographics of a potential slave workforce were provided, and convenient routes for deportation were found with the help of these censuses.
Now comes the ethical question for modern genealogists: Should we use these censuses in our research?
The question parallels one which confronted scientists and physicians in the past. The Nazis conducted inhuman experiments on their victims—experiments which could not be replicated without violating codes of personal and professional ethics. The question to be answered was, Should we use data derived from these experiments?
In genealogy the question takes on a special significance, because the people who would benefit from the use of this census data are the very people Hitler targeted for extermination. The 1939 census is an invaluable source of information for Jews tracing their ancestry to pre-war Germany. For many families, it is indispensable.
As genealogists we are historians, and as historians we cannot afford to overlook useful data. An African-American genealogist who refuses to use records created by slaveholders will find his path blocked at every turn.
Perhaps the proper approach to such records is to consider their use a protest against and repudiation of their original purpose. Using Nazi census records to perpetuate the history of a family once marked for destruction may be the best way to spit in the eye of evil.