Social responsibility.
Covid can't live long outside a host, and it absolutely can't reproduce outside a host. It uses the host's cell reproduction mechanisms to reproduce. IT CANNOT REPRODUCE ON ITS OWN. That's why the virus infects you, so that it can reproduce, and its species can continue to exist. Its niche is to use the host's cell reproduction mechanisms to reproduce.
If we had strong herd immunity, then covid would likely become something deadly but manageable, because the spread would be limited and slower. Mutations would slow, because the mutations would have fewer opportunities to persist.
Everything that reproduces experiences genetic mutation. "Mistakes are made." Most mutations don't persist and don't have much effect. Some mutations cause the organism to die or otherwise fail to reproduce, limiting the mutation's persistence.
Some mutations do persist. Red hair. Downs syndrome. Etc.
The "life cycle" of a virus is very short and very fast. Anyone infected with the virus gives that virus an environment to reproduce, and to mutate. A lot.
All the variants we have, including Delta, which won't be the last, are because enough people gave the virus an environment to thrive.
If you are infected, even if you have no symptoms, then you are providing the virus a safe haven to reproduce, thrive, and mutate. And you will spread it to others.
As for immunity, we have two ways to acquire it. With the vaccine, your body produces an immune response without having to host, increase and spread the virus.
Without the vaccine, if you're infected, and you don't die, then you'll likely have some immunity. But you've also spread it to other people, who may die from it, and who will further spread it. And you'll all probably contribute to the next mutation.
"I'm not vaccinated, and I never got the virus." Maybe. You could have been infected without symptoms, and therefore you did spread it, possibly killing one or more people.
"I got covid, but didn't go to the hospital. I beat it!"
Or,
"I got covid, went to the hospital, but recovered. I beat it!"
No you didn't. You spread it to other people, and helped it mutate into something stronger and more deadly.
"My $PERSON got it, and died in the hospital. But that was their choice, it didn't affect anyone else."
Yes it did. They spread it to other people, and they consumed medical resources and staff that could have been used by other covid and non-covid patients.
It's not just you, it's the people around you that you will infect, and all the follow on results.
Get the fucking vaccine.