When something crosses the line into bigotry and the like, I will generally call the person out if it's a friend or relative. One of my aunts once reposted (inadvertantly) one of those "clever" death wishes to our President - I coolly inquired as to whether she really meant it, and she realized what it actually meant, apologized, and took it down. A cousin reposted something rather crude about a particular religion, and I pointed out how insulted he would be if someone made such a display about his faith. He didn't get it, but at least there was no doubt that some of his family did NOT consider it okay.
When it comes to bigotry or advocating violence, I think complete silence is not enough.