I've heard this argument many times before and I'm well aware of the evolutionary mechanism behind strain resistance. However, I really have to wonder how much of this is just fear-mongering. Do we really believe that biotechnology will not keep ahead of this problem?
I think that rather than focusing on coming up with new chemicals to kill bacteria, pharmaceutical companies should work on entirely new ways of fighting bacteria, like genetically modifying bacteriophages (viruses that infect bacteria) to go after certain strains.