It has been used in studies to induce mutations in bacteria. It denatures protein, impairs proper structural formation of young eyes, creating permanent damage. SLS can damage the immune system. It can cause separation of skin layers and cause inflammation to the skin. These are toxic ammonium compounds.
Ingestion can be fatal.
Way back in 1938, when the FDA published guidelines regarding suitable levels of ingredients in products for human use, little was known about long-term exposure. I'm certain there will be more studies - but many years will pass. We all know debate and legislation progresses at a snail's pace. And the health consequences associated with continued use will escalate. Even when the FDA has all the scientifically valid, conclusive proof they need, they may only be able to require warning labels.