Herd immunity works to make the mass immune but it also means the loss of life in the weak, vulnerable and those with underlying health issues because there’s no system in place to protect them.
Also the surge of infection in herd immunity will put pressure on the health services and those effected cannot receive sufficient care.
Delaying the process is a longer process of infection which means that there is no manic surge in care and mass deaths over a short period.
There is no way of stopping the spread of the virus but only delaying it so it’s more equally spread over the year or so. To ease pressure on healthcare system and the medical profession. The delaying method also means better care can be given to those infected. therefore less deaths in the long run.