Several recent studies conclude that an increase in the pathogenicity of SARS-CoV-2 cannot be ruled out. However, this does not mean that increased pathogenicity is probable. Note that SARS-CoV-2 is a "direct" respiratory virus - meaning it is usually spread by the respiratory route but does not routinely pass through the lymphatics like measles and smallpox. Moreover, it is not normally spread by the fecal-oral route. Providing its tropism does not change, it will be unique if its pathogenicity does not decrease over time until it becomes similar to influenza and common cold viruses. As pointed out by Ewald in the 1980s, most respiratory viruses, unlike many other viruses, benefit greatly from the mobility of their hosts, creating a strong selective pressure favoring respiratory virus strains that cause only mild symptoms. In this review, I discuss the biological factors that tend to reduce the pathogenicity of respiratory viruses, including sensitivity to heat (which means the virus is less likely to multiply in warmer areas such as the lungs) and alterations to the cleavage sites and binding domains on the virus's surface proteins. Increasing immunity within a host population may increase selection for mild strains. Conversely, several biological factors could potentially increase respiratory viruses’ pathogenicity. These include the virus replicating in the lymphatic system, spreading via solid surfaces, and transmitting through fecal matter, including contaminated water. Furthermore, human activities and political events could increase the harmfulness of SARS-CoV-2. These include the following: large-scale testing, especially by methods where the test results are delayed by one or more days, such as PCR tests; the spread of the virus in settings where people are close together and not free to move around; poor hygiene facilities in developing countries; and social, political, or cultural influences that encourage people to remain socially active when they are sick, including political crises such as wars. If we can avoid these and similar eventualities, it is likely that SARS-CoV-2 will evolve to become milder, eventually becoming another common cold virus. However, the timescale is uncertain. Observations of previous influenza and influenza-like pandemics suggest that in the absence of effective medical interventions, it may take two or three decades for the virus to become indistinguishable from other cold viruses.