I think you need to clarify your question a bit -- are you speaking specifically of the Horizins program, or in general use of an established freelance editor to help you with self-publishing? Because the two are vastly different.

The argument against self-publishing (dreck or otherwise) is that it requires the writer to be a small businessperson in order to actually accomplish anything other than spending money, and that a) is a tough thing for most people to do and b) keeps the writer from their most important job -- writing the next book.