Recent graduates are encouraged to mention involvement in student organizations when applying to jobs; leadership roles in those organizations might speak well of a candidate. People might also put this information on a résumé because they want to work somewhere where they know they will be welcome. I am a teacher and I would certainly mention on my résumé that I am the faculty advisor for the Gender/Sexuality Alliance (even if applying to an engineering position). I am proud of my involvement as faculty advisor, and I also would not want to work somewhere where my sexuality would be considered any sort of liability.
Rather than expect applicants to take measures to whitewash their résumés (which also gives an advantage to those applicants whose extracurriculars are already "generic," i.e. upper-class and white), it seems we should be educating employers to be aware of their biases when reading these résumés, and teaching strategies for overcoming them.