The ones advocating it do know that well enough, and they are not going to do anything much personally. They are hoping to "encourage" some not so sharp follower of theirs to take them seriously and do the deed, or fail to do it when some white person will defend themselves or others, like Penny did, so they would then have another "martyr" ala Floyd or Neely for them to use.

With luck perhaps one day more black people will start to figure out that people like that are NOT their friends or doing anything much for them as a group, they are using what they claim is their "community" or "their people" for their own ends, and most of them probably see their own followers either as something like useful fools, or as subjects whose main purpose is to glorify and enrich those "leaders".