The thing is, it’s not a blanket statement of what must be done. It’s a principle that is guided by the combination of logic, emotional control, and, as strange as it may seem, empathy.

It stands as a metric to process one’s actions and choices. The individual vulcan accepts that the needs of all vulcans as a whole are more important than their own needs. This doesn’t mean that there is no debate. It’s the framework for the debate.

As the individual vulcan weighs options, they seek to determine what is the most benefit, and therefore the greatest need. They use logic to measure opposing or contradictory options, but they also consider the non physical ramifications.

Expanded into the federation, it becomes a measure for all sapient beings, not just vulcans. And that’s where the empathy of vulcans comes in the clearest. They’ll weigh the emotional harm to emotional beings as a need that must be factored into a decision.

But it also includes as part of their culture that no single vulcan is perfect, and that logic is a tool that must be developed. They can disagree with the decisions made about what the needs of the many are. It’s just that every individual sees the logic of their own needs being secondary.

It’s an expression of the vulcan equivalent of religion