They didn't read it then. I read it a while ago and from what I can remember there was nothing about manipulation or dishonesty. In fact I'm fairly sure manipulation and dishonesty were explicitly discouraged.
I never read it cover to cover, but paged through some random parts and it certainly contained guidance away from authenticity and towards identifying and saying/doing the right things to achieve your goals.
It's not a bad thing to read though, but more in terms of understanding what your competition is reading and tools they're potentially weaponizing (lots of copies have been sold). Just like I recommended my sister at least skim The Game when she was frustrated by her post-divorce dating experiences, which based on her description were at least partially being influenced by assholes having read it.
I feel like you might be unfairly judging the book by its cover (or title?). I'd be happy to be proven wrong if you can cite some examples of what you claim. I'd like myself to cite some passages where manipulation is explicitly frowned upon:
> Of course flattery seldom works with discerning people. It is shallow, selfish and insincere. It ought to fail and it usually does.
> Looking at the other person’s point of view and arousing in him an eager want for something is not to be construed as manipulating that person so that he will do something that is only for your benefit and his detriment. Each party should gain from the negotiation.
> The difference between appreciation and flattery? That is simple. One is sincere and the other insincere. One comes from the heart out; the other from the teeth out. One is unselfish; the other selfish. One is universally admired; the other universally condemned.
> If we merely try to impress people and get people interested in us, we will never have many true, sincere friends. Friends, real friends, are not made that way.
> If we are so contemptibly selfish that we can’t radiate a little happiness and pass on a bit of honest appreciation without trying to get something out of the other person in return - if our souls are no bigger than sour crab apples, we shall meet with the failure we so richly deserve.
> So let’s obey the Golden Rule, and give unto others what we would have others give unto us, How? When? Where? The answer is: All the time, everywhere.
> Be honest, Look for areas where you can admit error and
say so. Apologize for your mistakes.
> Promise to think over your opponents’ ideas and study
them carefully. And mean it. Your opponents may be right.
I think the main message of the book is to "put yourself in the shoes of others". And that definitely does not create dishonest, manipulative, self-centered pricks.
Empathy is an important part in understanding how to manipulate others. Without being able to put yourself into their perspective it's difficult to determine what actions will have which effects.
People over/misuse the word empathy, often conflating it with sympathy and/or compassion, when they're very different things.
A book can teach empathy while guiding people to be manipulative or exploitive of others. Just because you're able to see things from another's perspective (empathy) doesn't mean you'll give a damn about them or feel what they're feeling (sympathy).
Learning to separate empathy from sympathy with a conscious choice is part of adulting, a facet of establishing and enforcing (emotional) boundaries.
Those who lack that ability are quite vulnerable, it's one of the most rampantly exploited human flaws. "Bleeding Hearts" are a hugely exploited demographic, where people largely experience reactionary emotional sympathy and effectively lack empathy as a distinct observation they may then deliberate on what response is appropriate.
The psychopaths are the ones who either after deliberation never care, or can't even bother to deliberate on what they're seeing, which to the observer is tough if not impossible to disambiguate from a lack of empathy. Psychopathy is a pretty blurry thing though IMHO.