It’s reasonable for Delta or any employer to charge extra health care costs for unvaccinated employees since there are many more hospitalized COVID cases among the unvaccinated than the vaccinated. It’s fairer for an employer to charge the unvaccinated to recover a disproportionate share of their medical costs than to raise the health care premiums for all employees.
Studies and official CDC guidance show that the vaccinated as well as the unvaccinated can transmit COVID so everyone wearing masks (N95, KN95 or equivalent) makes sense until positive tests and hospitalizations drop significantly.
No matter what the airlines say, it’s still risky to spend time inside a metal tube breathing air expelled by many others who may be carrying COVID. The best air filtration system in the world will help reduce, but not eliminate, the risk and we all know that not every airliner has the best air filtration system. Even if you are vaccinated, you can still pick it up and transmit it to someone who might be more fragile or an unvaccinated child.
As far as I know, only an antibody blood test can determine if someone has a degree of immunity to COVID so people who believe that they are immune without an antibody test are fooling themselves. I know four people who thought that and caught COVID.
Many of the anti-vaxxers must be too young to remember smallpox, tuberculosis and polio. I grew up in that era and the only reason that we don’t still have them is because of vaccinations.