I have watched several Beheading videos that appear to be fake in my opinion. Facebook has a search feature that enables me to view such news stories in one location from many sources. Perhaps a warning can be presented. People who don't wish to view the videos can opt out.
There should not be any videos of severely violent acts allowed on social networking sites. Some may say that it is a good way to get the information out to the masses quickly and easily, but there is a sensitivity factor that needs to be considered. As a society, we try not to publish horribly graphic images out of respect of the individual and their families.
Videos of beheadings and other violent acts should not be permitted on social media or other websites from which children are not typically restricted. This type of violence is extreme and unacceptable. Furthermore, it is a crime in the United States. If videos of other criminal actions are prohibited or restricted, videos of beheadings certainly should be also.