Neo-classical economics suggests that it is, in fact ethical to get as much money as possible out of your customers.

Not because people should only care about themselves, but because redistribution through the tax system, and charitable giving, are far more efficient at producing net gain for society, than being "nice" to your customers.

Competition is what prevents people from being "gouged" when it comes to the necessities of life, and in the absence of competition, yes, government intervention is justified.

While the author is a monopolist ex post, in that once he writes his book, he has a monopoly, the market is competitive ex ante, in that anyone can choose to write a book on that subject matter.

So it is almost certainly justified to maximize profit, just as it is in most other businesses.