Let's suppose that in an antibiotic-resistant future some, very small, number of people develop a mutation that produces 2 effects: antibiotic resistance and VERY ugly nose warts. Since other people live for 25 years and the uglies for 100 years, I suppose they would be desirable mates with lots of offspring despite the ugliness. In a few centuries, they would be the majority. Now, if there weren't the antibiotic resistance, do such mutations have the same chance to appear? Yes, but they'd have hard trouble finding mates. Their mutation has only drawbacks, and no advantages. As soon as the advantage appears, the mutation has more chance to spread through offspring. The same with bacteria. It is not necessary that they mutate more, it is just that those mutations that help the bacteria survive spread quickly. But if the danger is not present, the mutation is not significant.