The idea being debated
Some people say humans deserve more consideration because they have something "special" that can't be seen or measured. For example, that humans:
- were created in the image of a god;
- have a special relationship with that god;
- have an immortal soul;
- have their own special "dignity";
- belong to a higher category of being.
Problem 1: it can't be proven
Nobody can check who has a soul and who doesn't. If it can't be proven, it also can't be used as a rule for deciding who can be locked up, hurt, or killed.
Problem 2: it doesn't explain why it would matter
Even if humans had a soul, why would that change how much a pig's pain counts? People who use this argument usually don't explain the link between the two.
Problem 3: there are reasons to think it doesn't matter
What makes it wrong to hurt someone seems simple: hurting someone is bad for the one who gets hurt. Pain is bad for whoever feels it, soul or no soul. An animal feels fear and pain all the same.
A comparison
Imagine someone said: "Only people born on a full-moon night deserve not to be mistreated." It's impossible to check, it doesn't explain anything, and it has nothing to do with feeling pain. Metaphysical standards have the same flaws.
In short
- A soul, dignity, or divine creation can't be proven.
- Even if they existed, they don't explain why an animal's pain would count less.
- What makes it wrong to hurt someone is the harm it causes the one who feels it.