Maybe not as dangerous as a stead diet of McD's. See it in persepective. He's at least trying, not just stuffing his mouthhole with salt-sugar-fat crap.
A steady diet of McDonald's (or any equivalent fast food) isn't nearly as inherently dangerous as things like "Super Size Me" would have you believe. Morgan Spurlock was eating 5000 calories of McDonald's a day, with most of it coming from the milkshakes, not the solid food. If you force-feed yourself 5000 calories of anything every day for a month, you're going to have health problems.
The "Fat Head" movie is good response to the "Super Size Me". It proves that eating at McDonald's isn't as bad as one might think and it also presents a lot of other interesting stuff.
Nobody is claiming steady McD's is healthy. There are actually people on the OP link and this thread who are posting that they want to try his system. That's what is scary.
This paragraph from his blog:
"I feel like the six million dollar man. My physique has noticeably improved, my skin is clearer, my teeth whiter, my hair thicker and my dandruff gone. My resting heart rate is lower, I haven't felt the least bit sickly, rare for me this time of year. I've had a common skin condition called Keratosis Pilaris since birth. That was gone by day 9. I used to run less than a mile at the gym, now I can run 7. I have more energy than I know what to do with. On day 4 I caught myself balancing on the curb and jumping on and off the sidewalk when crossing the street like I used to do when I was a kid. People gave me strange looks but I just smiled back. Even my scars look better."
Do you really trust this? Sensationalist at best. He's claiming that the diet helped him read a geometry book in one weekend and a string theory book in one sitting and a bunch of other mental heroics. How on Earth do people not see this as too good to be true?
He's apparently even willing to ship you a batch of his own concoction for free if you agree to try it out for a week with blood tests before and after.