A reader sends me a couple of examples from his local newspaper further helping explain why hyphenated surnames are receding from fashion among the educated classes in America:
"Jose Torrez-Gonzales, 28, and Marcos Gomez-Perez, 21, both illegal immigrants from Mexico" were arrested for stabbing a woman to death in a Walmart parking lot.
"A man charged with fatally stabbing a New York woman during an apparent carjacking attempt in a Walmart parking lot has pleaded not guilty. Luis Rodriguez-Flamenco was arraigned Wednesday in Albion Town Court on a charge of second-degree murder in the death of 45-year-old Kathleen Byham."
The use of a hyphen would appear to be an attempt at assimilation to American norms, since the Spanish tradition is to not use one. For example, actress Helena Bonham Carter, whose maternal grandfather was a Spanish diplomat, doesn't use a hyphen while her distant cousin actor Crispin Bonham-Carter does.
On a more philosophical level than Walmart parking lot stabbings, I would argue that all surname traditions will be inherently unsatisfactory in some sense or another because the reality of sexual reproduction is incompatible with our feelings of individualism and desire to be remembered as an individual. From two-to-the-nth your genes have come, and, if you are lucky, to two-to-the-nth your genes shall return.