I appreciate your point and I don't disagree with you (+1). However, the issue is complicated and I wanted to present another side to the original post. I thin

I appreciate your point and I don't disagree with you (+1). However, the issue is complicated and I wanted to present another side to the original post. I think it's likely that those two claims are mostly true in bacteria. Since bacteria evolve quickly and have experienced a lot of evolution, I believe they are likely near-optimum and therefore the second claim (IMHO) follows from that: changes would typically be deleterious. On the other hand, even allowing for that, it's possible we could be allowing them to escape a local maximum and reach a more-optimal state. And, there is a more significant criticism you could make: Even if I am right on both points, a population that evolved to be heterogeneous (with some small percentage of wildtype being resistant) could likely have the best of both worlds ;)