[wtallis]

> That begs the question, shouldn't we be more focused on promoting strong immune systems?

No. There's no general solution to the problem of compromised immune systems, because there are many different causes. Some of those causes are infectious diseases that can be controlled through vaccination, so translating your feel-good goal of "promoting strong immune systems" into specific courses of action will include using tools like mass vaccinations. There are no better or more cost-effective ways to prevent diseases like measles, and almost every unvaccinated person exposed to measles develops the disease even if they have a healthy immune system.