The bigger problem is that many potentially evil things are really cool.
Further - and while this is an entirely normative claim - if you would happen to agree that if you could save 1,000,000,000 lives by torturing one person for 5 seconds, that you should do so, then I would argue that torture is not inherently evil within your own normative value system.
It wouldn't be a 'vaccine' if it was in a vacuum, it would just be a vial of fluids. Once you have enough context to define vaccine, you can demonstrate that it is good.
>1,000,000,000 lives by torturing one person for 5 seconds
This argument is just obnoxious. Give me a moment.
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You can play with all the numbers you want, they don't change the underlying act. Except to the extent that you make the time period so short it no longer qualifies as torture and you're not even asking a question any more.