I don’t know why people are reading so much into this. People join groups on facebook for many different reasons, not all of which signify endorsement of the group’s message. For example, many anti-Israel people routinely join pro-Israel groups to either spread their propaganda or argue/debate with the other people in the group. And of course there is the JIDF, whose members apparently scout out hateful content in facebook groups and report it to facebook to try to have it removed. Or they somehow end up taking over the groups themselves and remove the group that way. Then of course there are people who join groups for other reasons, like learning what the advocates of various positions have to say — one could call it research or sheer curiosity. Others join groups simply because their friends “invited” them and they clicked the OK/Join button. Most people rarely even look at most of their groups and a lot of people don’t read the full descriptions of the groups they join. The JIDF recently succeeded in getting facebook to remove a group that purported to support fighting cancer — which had over a million members. If one read the group’s description though, it was full of vile anti-Semitism and conspiracy theories (thejidf.org). Unless we see Robert Spencer posting supportive messages in a group like this, I wouldn’t pay it much attention.