I really, really don't get why some people have such a big issue about UP.... Why the hostility? The weirdy defensiveness?
Excellent question.
I'm one of those people who felt demoralised and confused by reading the book. I own a well-read copy, I'm supposed to be quite intelligent, there's lots and lots I don't understand or that seems contradictory, I don't quite get it.
I like what ThisisYesterday said about how she interprets UP, I find it hard to know which parts of UP I'm "allowed" to interpret and which are core inviolable principles. I find it annoying that Kohn undermines so much and signposts so little (so little signposting I could see). People like ThisIsYesterday seem to fill in the gaps comfortably for themselves, I can't see anything but Gaps.
I have never met anyone IRL who has even mentioned UP, much less done it. My "hostility" comes straight out of how confusing I found it.... and how amusing I find online threads where people have tied themselves up in knots about how to "practice" it.
I once (foolishly, am very foolish) got embroiled with an online UP thread where I described a solution I found to get DS to wear his school clothes (chocolate raisin bribe). Oh no, the Devotees cried disapprovingly, you should A) put different clothes (like I want to massively challenge the school uniform code?) B) talk with him at great length about why he doesn't like his clothes C) consider sensory issues that need expert consultation and assessment D) Cut out labels from clothes E) take him to the shop to consider the various clothing choices (etc.). It went on and on.
WhY??? Who has the time for all that? When one chocolate raisin the first day back at school will do the trick? Why make me feel bad about it? 
I think I'm the same about Gina Ford, really; her approach reassures some people perfectly but it just made me feel crud & then angry.