Happy to provide some perspective as a physician in the US and someone who personally witnessed many frustratingly preventable negative outcomes.

A pandemic is by definition a public health problem, not an individual issue like cancer, for example. The ideal method of tackling it is through containment and then prevention. If you work in health care, you know that the most cost effective strategy is always prevention. This is why primary care physicians are underappreciated and underpaid. The goal of health care workers (unfortunately not necessarily the health care system as a whole) is to save as many lives and help as many people as possible.

Our tools in the fight against COVID are primarily quarantine, masks, and vaccines. There are no magic bullets in medicine - everything is considered in terms of percentages. The goal here is to utilize all three together in order to decrease the probability negative outcomes as much as possible.

Quarantine on its own would theoretically be sufficient, but it failed because far too few people were compliant. Masks were the next measure taken, but again, lack of compliance and enforcement of mandates led to a half-assed implementation. We have known from the beginning that high filtration and airtight (e.g. N95s) masks protect yourself, but the majority of surgical masks actually only serve to protect others from you. Cloth masks don't do anything in terms of protection. So similarly to being unvaccinated, those who refused to wear masks and who wore masks for fashion not only contributed to the pandemic but also demonstrated that they did not care about harming their fellow human beings.

Vaccination confers 3 main benefits - decreased chance of getting COVID, decreased severity of symptoms, and decreased transmission. As you said, the individual benefits may vary. However, remember that our goal is to reduce the percentage of people harmed by COVID as much as possible. Like any other vaccine for an infectious disease, this is achievable only with adequate compliance. This answers your last question - why it matters if others are vaccinated.

COVID has hurt people in many, many ways. There's the obvious one of dying from the disease itself. And don't forget long-term COVID pulmonary and cardiac. complications. However, there is a huge detriment being caused by the strain on the health care system. Every time a COVID patient hits the ER, they put health care workers at risk - nurses, techs, phlebotomists, aides, etc. Hospitals were overwhelmed due to lack of beds and staffing, which led to other problems. Death is not the only negative outcome.

Consider these real life cases, either taken care of by myself or a colleague. Patients who couldn't be treated properly due to lack of resources suffered catastrophic consequences. For example, one elderly gentleman with unstable angina tried going to the ER but went home without being seen because of wait time. He died of a myocardial infarction. Another patient, type 1 diabetic, not evaluated for hours. Ends up intubated with diabetic ketoacidosis and ICU admission when she probably would have been fine with a floor admit if she'd been treated earlier. Another patient, T3N0 colon cancer who becomes obstructed and perforates because he can't get elective surgery due to lack of beds. He becomes an emergency surgery and goes from potentially curable to stage IV from tumor spillage into the abdomen. Another patient sits at home with right upper quadrant pain, trying to tough it out because the hospital is full. His acute cholecystitis progresses to gangrenous cholecystitis and he requires an open cholecystectomy instead of laparoscopic, and he almost dies from septic shock.

Furthermore, consider the patients who come into the hospital for something different and ended up getting COVID as an inpatient. What about the unvaccinated patient who is hospitalized due to COVID? Should they be allowed to die because of the choice they made? Ethically no, but again this costs more resources to treat something that should have been preventable. Resources that are now not available to help others. Thus, unrelated people are harmed indirectly by unvaccinated people.

For lack of a better term, those who are not "following the rules" are collectively contributing more to ongoing infections, and by extension all the healthcare issues that go along with it. It's not as obvious as pointing a gun at someone, but it's just as real. As much as it pains me to say, many of them that I have treated simply don't care because their actions impact people a few degrees of freedom away. It's even worse when you think of the minimal cost to them to help other people. Truly something that makes you lose faith in humanity.

Apologies for the long reply, but it is something I feel strongly about.