That book is most likely referring to the inherent dangers of using light loads of slow burning powders in the 243...it was once well known for being quite unpredictable with such loads...the danger is still there, just maybe not as well known...stick to good (recent) load data, never use less than the listed minimum or more than the listed maximum of any given powder....and you'll be fine, the 243 is a fantastic little round.
I recommend H4350 for any bullet 90 grains or more..and Varget for the lightweights...the only 2 powders you'll ever need.
I've been loading for the 243 for quite some time...it has long been my choice for anything varmint...groundhogs, crows, coyotes, etc.
I never personally cared for it for bigger game such as deer...but I have used it as my kids first deer rifle, a role in which it fits prefectly.