I can appreciate your dilemma, a friendship of more than ten years is a life treasure. A lot depends on how you weigh this person's positives against his negatives. You mentioned that his Facebook postings are "disturbing." If his postings are the typical pejoratives, he might be open to an inquiry from you. If his postings are particularly vile and/or threatening, he may regard your inquiry to be offensive. I hope you are able to preserve your friendship.