I think you're missing his point. The immunity or resistance to antibiotics isnt with the people actually taking the meds--its rather that the bacteria have already gained resistance/immunity elsewhere before infection. Many of the more common antibiotics wont work at all on the resistant bacteria when people actually do get infected with the resistant strain. Its pretty much known that resistance to many ABs has been gained from overprescrips i.e people taking them when not needed etc.
Yes, that's a good point - it's the bacteria not the people's cells. Stupid for me to forget that.
As for "over-prescribe" - so should we not prescribe at all, let them get a bit sicker, then let them fester in permanent nagging debilitating symptoms?
What do you do? Heck, do you even know that what the person has is "resistant" until you try? If you don't do anti-bio's, what else do you do?