How is antibiotic overuse a bad thing?

If you overuse it then when you really need it, it won't work. The reason is that your doctor should do a culture, like a throat swab, and run a sensitivity test to see if an antibiotic is needed and which one will affect the microbe. You want to hit the microbe with accuracy and not with a "shot-gun". When treating the microbe with the right drug, the persons' normal flora will not become resistant to that antibiotic. I get really upset if a culture and sensitivity isn't done because the antibiotic may be needed to knock a microbe out and now it will not work at all or have to be given higher doses.