I've been on nearly 20 cruises and although the things you mention are true, it seems the author is biased and trying to make it seem worse than it is.

TLDR: I love cruising, it sounds like the book is over-sensationalized, but cruising isn't for everyone.

I was also enlisted in the US Navy and my ship did a 6-month WestPacific cruise. On land many military jobs are 8 hours M-F, if you do shift work it is usually 8-hour shifts as well. In port, I worked a typical work week. As soon as we set sail our work hours changed to either 12 hours on 12 hours off or a 16-hour workday 7 days a week, with reduced hours on Sundays. Boredom and unstructured time are not good for people who are confined to a small space.

If you look at the ratio of passengers and crews on most cruise lines you'll see that there is usually 1 crew member for every 2-3 passengers. Not all crew member's jobs are directly related to the customer's experience, there are entire departments dedicated to cleanliness and maintenance. Because most ships have services 24/7 it is perpetually being cleaned and repaired.

Although the vast majority of cruise lines are registered under foreign flags that doesn't mean there isn't a standard they are required to meet. For a cruise ship to take on passengers at US ports the US Coast Guard requires them to meet the International Convention for the Safety of Life at Sea (SOLAS). This is a strict set of rules to ensure passenger safety and crew competence. The one cruise ship that I'm aware of that flys under the US flag is the NCL Pride of America which cruises the Hawaiian Islands. The Jones act requires any non-US ship to visit at least 1 foreign port on each sailing. This ship had a primarily American crew and although the ship was practically brand new, it was the dirtiest and worst maintained ship I'd ever been on, and that includes the 40 year old US Navy ship I spent 2 years on.

On most itineraries, you are in port for several hours most days. The ship is filled with activities and events all day, from live performances in the theater, dance lessons, cooking lessons, gyms, pools, spa, yoga classes, and a kids club, you can even attend AA meetings.

There is a Dr and a sickbay available on all large ships. I'm not sure what size the ship needs to be for this to be a requirement. Keep in mind that seniors are a large part of the passenger list on many cruise ships. They have the ability to medivac people from the ship if needed.

I've never been concerned about food-borne illness, of course, this can happen to any restaurant, but to have passengers get sick from food would not be good for business. The world is too connected these days. There are entire businesses dedicated to reporting on each sailing of each ship. There is a problem with some viruses, for example, Norovirus is common on some ships and once a ship gets infected it is a big challenge to irradicate it from the ship, because the ship is never empty, they are moving passengers on as they are moving passengers off. You can often find which ships are having this problem ahead of time and take precautions or avoid the ship. We experienced this on a cruise a few years ago.