Hi Jarvamundo & All,
The way science basically works is that someone comes up with a theory that best explains a set of facts. They go away and find ways of experimentally testing the theory, perform the experiments and see if the results further support the theory. In this way the theory becomes the "standard model" -- that's not to say it's absolute fact but it is the best theory that passes the Occham's Razor test. For example the Big-Bang theory is the "standard model".
Why is it the standard model? Put simply, it explains all the observed facts in the simplest way and makes the fewest number of unsupported assumptions. If evidence comes to light that disproves a model, then the model is either modified or discarded. If over time a theory has withstood everything thrown at it, it tends to harden into "fact". Fred Whipple's theory has undergone some slight modifications but has stood the test of time well.
The Dirty Snowball model is at present, and by some distance, the best model that explains cometary behaviour. The theory of which you have spoken has little to no supporting evidence, is contradicted by a considerable body of observational evidence and (much less importantly) no-one of any standing in the field is supporting it.
When the proponents start to accuse NASA of certain conspiracies and cover-ups, their credibility takes a big hit in my and most people's eyes and ...
... when Immanuel Velikovski gets a mention (even a passing mention), I'm sorry, but my fingers go straight into my ears and I go La-La-La-La-La-La
Does this "plasma" idea pass Occham's Razor -- not by any stretch of the imagination.
Best,
Les D