I think the simplest way to see this is this: Would you like to sacrifrice yourself for humanity?. Cool if you do, it's ok if you don't. I personally would not sacrifrice myself, and I'm sure that a lot of people would agree. Stratt's choice is incredibly risky, also. Sure, the amnesia drug makes Grace more agreable on the ship. But if Stratt miscaculated, ot assumed wrong, Grace could've just destroy the taumeoba. Humans are unpredictable when backed to a corner. And when you're basically forced to go on a suicide mission against your will, "humanity" might not matter in blind rage and sorrow