There is no evidence of human health problems from yogurt with live bacteria, and there is some evidence the bacteria may be beneficial.
It is controversial whether yogurt bacteria survive in the gastrointestinal tract, and conclusions must await completion of research, but there is better-thananecdotal evidence that bacteria can help colonize the tract and keep out bad bacteria.
The theory is supported by studies of young chicks sprayed with bacteria present in adult chickens. The chicks take up these microbes and are not colonized by harmful salmonella, an effect called competitive exclusion.
There is no reason to eat only yogurt without live cultures for fear of danger from the bacteria that ferment milk into yogurt. The most commonly used culture is Lactobacillus delbrueckd buaricus in combination with Streptococcus thernwphilus.
Both are harmless in the gut, if they survive.