I like this analogy a lot. As High School Biology teacher I appreciate the cell reference. However, to continue the analogy, a cell that splits uncontrollably, and attacks other cells is called Cancer.
Agreed. I'm always fascinated how the macroscopic and microscopic worlds recapitulate one another (as above, so below). Where analogies break down is also interesting.
Splinter groups can be seen as mutations of a larger organism. As such, they can exhibit adaptive, neutral, or maladaptive traits. In some cases, they may actively attack or undermine the prevailing paradigm (Al Qaeda :: Islam). Some things become viral infections or other kinds of parasites, while others coexist quite peacefully or even symbiotically.
In my view, there is very little in sociology that doesn't have close analogs in (nonanthropogenic) biology, ecology, and evolutionary theory.