It's just an easy way for HR to indirectly socioeconomically or racially profile you. Have a clean cut picture of yourself on any easy to find US-based social media site to help stay near the top of the pile.
This seems like a pretty paranoid generalization. In my experience linkedin is more of a way for recruiters to just mass-email people that fit keywords so they can keep their numbers up. I don't put much about my socioeconomic status or race on my linkedin....