You completely misunderstood the context!
This is the exact extract from the book — not my invention. And if you read it carefully — there’s no sufficient source of Omega3s or Omega 6s in the day 1 of FASTING MIMICKING DIET PROTOCOL — that’s why the supplement. Omega 6s are essential fat that our body needs, great ratio to shoot for Omega 3s/Omega 6s 1:1 or 1:2. The problem with modern diet VS this protocol, is that people getting too many Omega 6s, like 1:20 and more! So you are right but you completely misunderstood the extract and also I want to say this again — Omega 6s are essential for health fatty acids, you need them in your diet. How you would get it? Get a capsule (or liquid supplement) of good quality Omega 3s and Omega 6s (sometimes there is also Omega 9 in some brands) with the correct ratio.
Hope this clarifies it! Thanks!