They just don't realize how mind-numbingly stupid they sound to homeschoolers.
You know the old adage "Better to be silent and be thought a fool than to speak and remove all doubt?" People who don't know anything about homeschooling and just form baseless opinions should be silent...because the minute they say anything about socialization they come across as fools.
I don't even acknowledge them anymore...the minute they start, I disregard them completely.