This, like most stereotypes, is built around a core of experience, and then expounded. With a lot of vegans, its often not that they're wrong about what they say, its how they convey it. This came up today in another HN discussion on smoking as well. Its ok for them to not like things, just don't be a jerk about it.
On topic, while I agree that we may very well all die, this can also be looked at in a different perspective. When the antibiotic in question was first introduced, it had effectively a 5/5 chance of working. After ten years, it then had a 4/5 chance of working. Like most power laws, in maybe 10-20 years, it will have a 3/5 chance of working, ect... with a decay rate that slows with time.
Like all evolution, antibiotic resistance is driven primarily by the rate of survival and reproduction in the population. If resistance against AntibioticA is a strong predictor of survival (like when its newly introduced, and highly effective), then lots of bacteria will develop the immunity. As it gets used less, due to limited effectiveness, then it will become less of a predictor, and less bacteria will multiply with that as a trait.
Its not like evolution is "free" either. Often times, if an organism becomes heavily specialized in fending off one threat, then they leave themselves open to invasive species or perpendicular threats. I firmly believe that we have intelligence (I really do) and that while natural evolution is powerful, we already have many of the tools necessary to understand, and adapt along with it. We just need to be able to understand why they're changing, how they're changing, and how we can exploit that process for our gain.