While he is respected for his coaching methods, research, and other contributions, much of Layne Norton's reputation was built upon him being a natural bodybuilder. Attacks on that status are meant to cast a shadow of doubt on the validity of his training and nutritional recommendations, and remove the illusion of "natural results" from products attached to his name.
For a lot of people of this site, it doesn't matter, they're intelligent enough to have realistic expectations of themselves and any products and programs used to reach their goals. Though there is an aspect to the fitness industry which enjoys a clear distinction between "nattys" and the morally dubious users of steroids. Programs, products, fitness and nutritional/supplement advice promoted to the audience is based on ideals of naturally achievable results - validated with a bodybuilder or athlete with a test proving they've never had a needle in their ass.
Any natural bodybuilder who is found out not to be is automatically forced to the other side of the fence. Along with a change in reputation, this means losing a fan base, clientele, and specific marketing opportunities which are all geared towards the increasingly lucrative natural bodybuilding and fitness circuit.