Why would anybody do that!? That's like taking the chocolate out of a chocolate chip cookie!
I switched to SLS-free (Squigle) about a year ago and couldn't be happier.
My wife suffered with ulcers all her life until a comment on the NHS website suggested cutting out SLS. She followed the advice and very quickly stopped getting ulcers. I mentioned it in passing to our dentist and he said he won't use a products with SLS in for himself or his family ...