HMMMM... haha. I love discussing satanism. It's intriguing.
The point that other tracts of Satanism that deviate from the Church are somehow "invalid" for their heresy is an interesting idea. Especially since LaVey's own daughter is counted among the number who have branched out. We saw this with the Christian Reformation, those who left were labeled 'false', but held on, and through sheer perseverance managed to form a distinct movement with longevity.
Another reason not to entirely discount splinter groups is that many of them (Think Temple of Set) are most certainly NOT athiest. They are what I would call, 'Luciferian' satansists, who seem to need and want a deity of some kind. Within that community, this is a really critical split! It would be different if they had just formed a C.os look-a-like organization, but they instead redefined the concepts of deity at the core of the belief system!
I love it.
And yes, the larger pagan community (in an attempt to be more socially acceptable and tolerated) had vociferously distanced themselves from the satanist community. But I'm not really an adequate representative of the 'community at large' , I compare the various groups and find that there is much in common. Rituals taking place in a circle, the calling of a deity (or the psychosemantics that emulate such an act), some of the lodge cermonial stuff, the casting of spells, the requirement to self improvement, (rather than simply "converting" through faith.), for me they are very, very similar animals.
And fascinating conversation topics!