There is nothing absurd about any of those scenarios. Those are perfectly valid questions, and to answer them might be difficult - that's why it's not at all obvious that 40 year olds are more morally "important" than 80 year olds (for me they obviously aren't). However, to answer the original question is very easy: Human > Rat. Defending the opposite position is absurd, and although some people might feel Human=Rat - it's a fallacy to compare this to "Black human = White human", or to "Jew=Non-Jew".
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There is nothing absurd about any of those scenarios. Those are perfectly valid questions, and to answer them might be difficult - that's why it's not at all obvious that 40 year olds are more morally "important" than 80 year olds (for me they obviously aren't). However, to answer the original question is very easy: Human > Rat. Defending the opposite position is absurd, and although some people might feel Human=Rat - it's a fallacy to compare this to "Black human = White human", or to "Jew=Non-Jew".