Probiotics, including bifidus can be very helpful for many people
but are risky for people with IBD, IBS, or autism.
This is attributed to biofilms and SIBO (small intestine bacterial overgrowth)
People with IBD, IBS, or autism have a high rate of biofilms.
SIBO is very common among individuals with digestive problems.
About 40% of people with IBS have SIBO which is also associated with
Relationship of Biofilms, Bifidus and "Good Bacteria"
Bacteria live together on the surface of the intestine in a BIOFILM. They help each other extract nourishment, mainly from the foods that we are not able to digest and absorb into the bloodstream. Inside the biofilm, "good bacteria" can mutate into pathogenic ones. (Elaine was very careful to limit the approved bacteria because she feared such mutations. Most people with IBD or ASD have biofilms in their bodies).
This is verified in Medscape.
"Biofilms increase the opportunity for gene transfer between bacteria and and among
them. This is important because those bacteria which are resistant to antibiotics may
transfer the genes for resistance to neighboring more susceptible bacteria.
Gene transfer has the ability to convert a previous avirulent commensal
organism into a highly virulent pathogen." 
Lewis K. Riddle of biofilm resistance. Antimicrobial Agents
The Risk of Bifidus and SIBO (Small Intestine Bacterial Overgrowth)
The medical school textbook, Biochemistry and Physiology of Bifidobacteria,
written by Anatoly Bezkorovainy, professor at Rush Medical College comments on this as well.
This book explains that bifidus is helpful for humans except under
certain conditions. One of these exceptions is SIBO.(small intestine bacterial overgrowth)
Bifidus tends to overgrow and cause fat malabsorption for people with SIBO. Many people with digestive problems have SIBO in their bodies
To view the comments inside the book regarding the risk with bifidus:
Scroll down the page until you see "Metabolic Disorders Associated with Bacterial Overgrowth."
SCD works effectively on many bacteria in a beneficial manner when the approved probiotic is used.