Rights. I love rights. Civil rights, human rights, animal rights. Gay rights, women's rights, patients' rights, consumers' rights. Rights are useful tools. But let's be honest: rights are just some shit we made up. Rights are an easy, deliberation-free way to trump potentially disastrous decisions, like, say, enslaving people. We made them up because they're useful to achieve something good.
But a lot of us think rights are real. People (and sometimes animals) have natural dignity, or inherent value, or some other shit we make up, just by being people (or animals) and we have to respect that magical feature of their existence. But the Universe doesn't care. Absent sentient beings to value themselves and other sentient beings there is no value, and absent people to take offense there is no dignity. Saying a person has inherent value just means we really don't like to hurt people. It isn't a metaphysical fact, a biological fact, another statistic like mass or density. The only measure of value is how valuable it is for someone.
Rights aren't the only shit we made up. Just about any exceptionless rule is a good candidate for made-up magical shit. "Lying is wrong." Sure, I can get behind that. You shouldn't usually lie. But why? Did we make that shit up? Either lying is just plain wrong and you'd better be honest when the Nazi asks you where the Jews are, or lying is only wrong for some reason. A reason like: because it usually hurts people. And if that's the case, it is the hurting people part that's bad — the lying is just how it happens sometimes. Which means that if lying, in a given case, actually helps people (like, say, those being targeted for genocide) it isn't, in fact, bad.
In the end, just about any moral rule boils down to if you do this, people usually get hurt. And that's great, we don't like to hurt people, so we should avoid it. But dogmatic adherence to these rules, this shit we make up to remind ourselves not to do the hurting thing that's actually bad, sometimes causes more bad stuff to happen. Personally, I think it is more important not to hurt people (or animals) than to let them get hurt because we thought the rules were more important than their reason.
But maybe I just made that shit up, too.