The first time I had them- I was 10 bear in mind, they frightened me. Because I had been taught that suicide is wrong, suicides go to hell etc. So- while it felt like a taboo thing to think about, it never felt 'crazy'.
I challenge anyone to experience 3 close family members die in childhood and get bullied constantly by a (suspected) narcissist and think life's great. It made perfect sense to me why I wanted the hell out!
Following on from that, life's been up and down but, it's been a lot of struggle overall. I simply don't buy that everyone has a good life by default and it's nuts to think differently. The quality of our lives vary enormously- all throughout life. I'd actually assume that a large proportion of depression is down to a person's situation. Including their history- childhood. You can't change that shit!
Besides, saying that is also saying that 'I like life' is the default setting on humans- maybe animals. Why? Surely, our default settings are: 'I will survive (and procreate.)' We don't actually need to be always joyful to do that necessarily.
A joyful antelope bounding across the plains probably missed the lion hiding in the grass. Isn't there science to say we are more wired to be affected by negative experiences? 'Oh, what a lovely sunset' won't impact your life so much as: 'Shit! Isn't that a snake?'
Of course, depression can affect people with very good lives. I think the whole classic: 'If the things that once brought you pleasure now don't' is going on then sure- maybe it is depression. Maybe it's worth trying some things out to cure it. That's not to say they will though... Maybe they're saying that to cover that demographic.
I'm guessing this book is irritating you?