They can provide a good environment for h. pylori to move
in. They can create autoimmune diseases. Yogurt generally has dead
organisms, because they are killed off in the pasteurization process, though some expensive yoghurts add some back in, and some people are so sensitive to dairy that it affects them adversely, not to mention that yeast loves the sugar in dairy, so a supplement is better -- the good ones contain billions of hibernating organisms if it has been kept under refrigeration.