Hi- I'm a very successful ebook writer that has used amazon as my platform for about a year and a half now. Their FREE KDP SELECT and now Kindle unlimited is only going to hurt REAL authors in the long run. First a kdp select handcuffs you to keep all you eggs in one basket and unless you are vested in a social media market plan personally, with a professional website and paid webmaster directing, you don't have a hope in hell of making money with Amazon as your own platform even if you are a gifted writer with niche knowledge and experience behind the scenes with Amazon.
The average person is only going to make a few dollars selling books on Amazon- less with KDP SELECT and this new "for the buyer" promo program. The rank increase for oodles of FREE promo books is minor. The reviews you get are from FREE buyers and they are often nasty- one or toe bad reviews from a FREE buyer having a bad day will KILL sales. Offering your books for free undermines the value of your writing talents and book value- the exact image you are building.
And the portion of the pot the author makes is peanuts to what a good book in a top niche with quality writing and professional marketing on 5-6 platforms would make when people actually see value in paying for an authors efforts and good book!
Check out my website for Even more. My life experience pretty much proves the perspective you are misleading naive authors with is dead wrong!
I think you better give them the other side of the coin too-