I am a professional writer and book author.
Imitation is an excellent way to introduce a skill and hone it. In learning art, imitation helps students get form and symmetry down. After they learn the fundamentals, they can find their personal artisitc 'voice', often more easily because they have a framework in which to work and this actually provides freedom. :) In learning handwriting or spelling, copying words down aids the educational process and helps the brain retain information. The same is true of writing.
I am a recent user of IEW and like the format for the grades for which I have used it-- 4th, 5th, 6th, 7th. I supplement with my own material (5 paragraph essay format for expository writing, creative writing assignments of my own design for that, writing real letters to the editor for practice in persuasion, etc. ) I don't think it's fair to call IEW 'plagiarism' because, well, it isn't. :)
If someone has a problem with the worldview of any instructor , then he should not choose that instructor to educate his children. I wouldn't choose any program which made me uncomfortable. I happen to find the worldview/framework that IEW provides quite refreshing.
I find IEW a solid program that produces excellent results, for what it purports to do. It cannot make your child a Pulizter prize author- your child has to have the drive, talent, skill, motivation, etc.. Different children learn best with different methods- I get that. But IEW can work great- but it's not the only program out there. If you don't like it and can't find something better, I suggest creating a program that works with your kids. I took what I liked about IEW and am cobbling together other things (as mentioned above).
I don't need government endorsed 'credentials' from Andrew Pudewa or any other instructor. I need results. His program has provided that for my children and that's all that matters to me.