Could you enlighten me to the pros and cons of this.
...
You mentioned the drug benefits....how so? And then you mentioned the dangers.
Pros: Need a drug or chemical manufactured in large quantities quickly and cheaply? Design a bacteria that eats something relatively mundane (corn mush for instance) and that poops what you want (most likely along with other stuff hopefully easily filtered out). Or how about a bacteria that eats staph infections?
Cons: Maybe you mess up and the bacteria that you engineered to eat staph and be nearly immune to antibiotics (so they could be used in conjunction) ends up mutating and instead of eating staph now eats flesh like staph. Now you just created a super-infection. Or maybe your corn-mush-eating-insulin-pooping bacteria gets into a farmer's corn field and turns it into insulin-on-the-cob and ruins the crops (maybe kills some people too).