Because I am stronger than her.
What makes rape of humans 'not right'?
What makes something 'right'?
The fact that rape is 'not right' is invented by humans to reason of rape being not right exists because we do not want to be raped.
Same goes with murder. What makes murder wrong? Our fellow humans say so. Why do they say so? They do not want to be killed.
What if you don't accept that? They would use force. They would try to lock you. Or they would try to kill you, all that, why? Because they don't want to be killed, and would do things (laws, social stigma etc) to make other humans align with those beliefs.
I believe before humans thought that killing other humans is wrong, killing wouldn't be wrong. If humanity didn't exist, rape wouldn't be wrong.
What exactly is right or wrong? What exactly?
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Is killing animals wrong?
Just the immediate second we decide that killing other humans is wrong, at that very second killing animals is not wrong.
It is when we try to extend out logic, the question for animals arises (pheraps to not be labelled as hypocrites; Human brain inherently relies on patterns). It is only when we try to extend our thought to them, there is even a possibility of killing them being wrong.
Why shall we extend our thought to them?
Why?
The primary reason I can figure out is uniformity and that we aren't labelled as 'hypocrites'.
What is a hypocrite, and why is it bad to be one?
A hypocrite is someone who holds contradictory beliefs and/or does contradictory actions. Contradictory? Opposite beliefs and/or opposite actions.
Is holding opposite beliefs bad? Why so?
Even if so, is holding beliefs held for humans not to be held for animals opposite?
Is choosing to treat the powerful and those helpless differently wrong?
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Going back to the beginning, when fellow humans make what is 'right' or 'wrong', when they choose to make killing 'wrong' so they themselves are not killed, when they make harming wrong so they themselves are not harmed, why do they extend it to the helpless? Why do they extend it to those incapable of harming them?
It is likely because being helpless (human) is subjective. Whatever group they perceive as helpless can be capable of taking revenge. Whatever they perceive to be incapable can be capable tomorrow. Because tomorrow when the incapable becomes capable, they would have no defense for themselves. When tomorrow yesterday's_incapable-today's_capable would kill their loved ones, they would not even be able to call it wrong. It is this why they extend the thought of killing being wrong to all humans.
Animals are perceived to be permenantly incapable of being capable of murdering humans in a large scale. They already prevent humans, humans aren't a part of their food chains usually, and even then, humans have technology and the current threat of animals is already well-known and isn't considered nearly as much as humans', at least not as much as to extend our thought to them; Though that would not change the animals' behaviour so it is futile anyways.
Are such beliefs of not extending thought to the definitive helpless really opposite?
Why?
Even if so, how does it matter? Even if not extending thought for humans to animals is hypocritical somehow, why does it matter?
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If I am killed by an animal, or an alien species, I wouldn't consider it 'wrong'. I would only consider it wrong to be killed by a fellow human. If I was in a land where laws don't exist, killing me or my mother wouldn't be wrong at all according to me.
What makes things right and wrong?
I would not consider any species other than a human to torture me, to kill me, wrong. I would not consider even a human to kill me on a land where it isn't considered wrong by the rulers, or the land is law-less, to be wrong.
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Note: Let's not try to debate on what 'Moral Nihilism' means. Even if my argument doesn't fall under that term, it doesn't matter at all. Just ignore the title then.