But there is a lot of harm in recommending more sleep. If someone only needs 6-7 hours but keeps trying to force 8-9, they're going to have all sorts of trouble.
I personally have an issue with a drifting circadian rhythm that makes it impossible to go to sleep at the same time every day if I sleep a full 8-9 hours a night. The cumulative effects of this gives me very poor quality sleep and negatively affects my social life. Changing to sleeping only 7-8 hours addresses this, and I've been testing the cognitive effects of this change to see there aren't any.
I think Walker's overall message is important, but the numerous fabrications and massaging of data he's committed to convey that message is bad science. If you tell a lie (2/3 of people are sleep deprived, if you sleep less than 8 hours you're killing yourself) to dispel another lie (you don't need more than 6 hours sleep, keep hustling and chugging 5 coffees a day), you aren't actually making things better. You're just replacing one problem with another.