The argument one frequently reads/hears on this is, that a virus has no evolutionary advantage to kill its host and if the virus becomes fitter in terms of in

The argument one frequently reads/hears on this is, that a virus has no evolutionary advantage to kill its host and if the virus becomes fitter in terms of infecting new hosts, they can neglect functions in their genome that lead to deadliness. A respiratory virus may have an evolutionary advantage if it doesn't hit the organism so hard that the host stays home and isolates. Mild symptoms may increase the likelihood for socialising for example, thus there could be evolutionary pressure for a milder form to develop. I would assume that these are just general observations and it won't allow a clear prediction where COVID19 variants are headed. But there are theories that other coronaviruses have been more aggressive initially until they became the milder forms that are nowadays endemic. Of course we know plenty viruses that have evolved and are still deadly, so this isn't something I would bet on.