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I think Grammar Geek hit the nail on the head (although I thought John stopped to help the lady paint her
face).
What you should not have is really a non-sentence, that is a sentence fragment, that starts with a
because clause and never introduces a main clause to go with it.
-- Why didn't you finish your spinach?
-- Because I don't like it. << This is the sort of
thing that is frowned upon. It's fine in ordinary conversation,
but not in a paper for classwork.
Nevertheless, for stylistic reasons, you will probably find that even this construction is used by some authors!
CJ