I'm related to the Leathers who changed their name to Palmer. One theory of the name change is that some Leathers were "gypsies" who engaged in theft, among other crimes. See an article by poet John Greenleaf Whittier which mentions them (http://www.wordiq.com/books/Yankee_Gypsies/8
I've been unable to find out what the last straw was that caused so many to change their names. It may be in the state archives in Concord; name changes were handled by the state legislature. Maybe someone closer to NH than me (I'm in Florida) can find out for us.
for a theory, though even fratricide doesn't seem to me to be reason for so many people to hide their family ties (doesn't everyone in a small town know everyone else, regardless of name?) Unless they were Quakers, which is highly doubtful.