Saying that parasites are the cause of all diseases is incorrect.
Think about it logically - if you took a human and raised him in a parasite-free biosphere free of any possible parasites, according to Clark it would be impossible for him to get any diseases, which is incorrect. Clark's statements don't even fit with the definition of the word disease. Do some parasites cause some diseases? Yes. Are all diseases a result of parasites? No. Everyone has parasites and you will never get rid of them all, even if you followed Clark's methods 100% (which is a near impossible feat in itself).
Do parasites cause Morgellons? Maybe they do, and if so you could likely be helped by some of Clark's protocols. But saying that Morgellons is caused by parasites *because all diseases are caused by parasites* is factually incorrect.