I've read in a few different places that the good bacteria/flora/probiotics in our bodies actually support our immune system. Start wiping the good stuff out, the immune system suffers, and the bad stuff starts to gain the upper hand. I think that's why it's so common for people to have candida overgrowth AND parasites together as a result of being poisoned with Antibiotics .
Anyway, once the immune system is crippled, needless to say everything else goes haywire. Bad bacteria/yeast/flora/etc. commandeers your body and everything gets clogged. So I guess my take on the matter is that wiping out probiotics/good flora is more than enough to send the body into a downward spiral. Gee, aren't we all lucky to have these wonderful Antibiotics available at our local doctor?