Even when a community has herd immunity, there are still individuals who won't have immunity within that group. Anyone who comes into the community with the vir

Even when a community has herd immunity, there are still individuals who won't have immunity within that group. Anyone who comes into the community with the virus can still spread it locally to the people around them - herd immunity only affects community spread, not individual spread. So when there's a pandemic raging on outside the country, free movement of unvaccinated people across the borders will necessarily mean that there will be cases domestically affecting the domestically unvaccinated. Until the entire world has herd immunity (a long time from now), if a community wants to drop caseloads to ~0, travel restrictions for the unvaccinated are one way to accomplish that. Whether that's just or fair or good policy, certainly up for debate.