The biggest problem for astronauts is the lack of gravity, not the excess of it. Lack of it creates problems for bone structure, muscle growth, and blood flow.
The author is merely addressing the logical consequences of inertial effects on space travel. No one will ever travel to Alpha Centuri in four years. Even the fastest probe ever created will probably take centuries to get there, but may send back photographs that arrive in four, if there is anyone around who remembers to look for them.
When I had a conversation with Frank Borman, he assured me that the toughest part of spaceflight was the 9G acceleration. Lack of gravity is not the same issue as g-forces.