A witch accusation (which is what some of this conspiracy theory stuff looks like to me) is sometimes functional. It acts as a social mechanism for revenge or whatever. In our culture though, a "witch accusation", along the lines of what we've just seen from our eccentric chums, is normally quite ambiguous. It probably has some propaganda effect, particularly on people who don't discriminate between Marx and Icke, but that's heavily tempered by the tendency to make the accuser look like a nutter in the eyes of a majority and to taint anything else they may say.
What seems to be missing, except in special cases like the 80's 'satanic panics', is the social apparatus that turns the "witch accusation" into an effective social action.