Is the evolution of bacterial pathogens an out-of-body experience?

It has long been believed that the complex interactions between pathogens and the hosts they infect are the primary driving forces that determine the strategies used by microorganisms to counter host defenses. However, new evidence suggests that the external environment, including other hosts, might have a greater role in the evolution of certain pathogens than previously thought. In particular, acquisition of virulence traits through horizontal gene transfer might occur at high frequency through microbial contacts in the environment, either as mixed microbial soups in the guts of insects or other vectors, or as soil or aquatic biofilms. Should microbiologists be alarmed about the unknown risks posed by bacteria gaining potentially dangerous traits from external environmental, or even extraterrestrial, sources?