Yes, some experts claim that dry food is harmful to cats, but it is hardly poisonous. Other experts, including holistic veterinarians, animal nutritionists, and other individuals who have studied cat nutrition, have indicated that there is nothing wrong with dry food when fed in conjunction with a high quality wet food.
Dry food alone may not be the best diet for cats, but dry food fed together with wet food can be a very healthy diet.
My own anecdotal evidence (hardly scientific, but my experience nevertheless) has shown that cats can live to be 19 and 20 years of age when fed a high quality dry food, complemented by a high quality wet food. The two cats I grew up with, who were indoor-only cats and ate dry food most of their lives, with wet food once a day, lived to be 20 years old, and 19 years old (died two months shy of his 20th birthday.)
My veterinarian here in Germany (vets over here don't have the same education as those in North America), who is a Tierarzt (veterinarian) as well as a holistic veterinarian, recommends a diet of grain-free dry food combined with wet food. I trust her experience, knowledge and education. My Sphynx is thriving on such a diet, as are the cats at his breeder's (a very small cattery, that only has one litter a year and focuses on health and personality in her kittens.)
The wet and dry food my cat eats are made from 100% organic ingredients, 100% free range, hormone- and antibiotic-free meat (chicken and beef) and sea-caught fish (no farmed fish). Pet food regulations are strictly enforced here in Europe, and have been in the EU ever since the mad cow crisis. All animal feeds, including pet food, have to be made with human-quality ingredients, and are tightly regulated and strictly controlled. So I am not poisoning my cat by feeding him dry food. I am giving him the best possible diet for his health.