Why is sentience a "go to" argument for animal advocates and vegans?
Animal advocates and vegans advance the argument that animals are sentient and this means that they should be afforded a particular kind of regard. Often this means some kind of interest-based rights, but I get the feeling that for most, sentience just means that other animals feel stuff so we shouldn't be harming them.
The problem of harm is one of welfarism - that is, if we can use other animals without harming them (except for the killing part that is) there seems no real reason not to do so if there is a benefit to us from this. In the end I think the argument against this kind of animal use is from a personal sensitivity point of view - someone feels uncomfortable or sad that another animal is killed for food for example. For most people it probably is the case that as long as there is some level of good welfare, the use of animals in this way is fine.
The rights question seems to me to be a bit harder to work out. Why does "sentience" mean we should afford other animals rights? Do activists seriously believe that mice should have rights? Or, at least, the same rights as a cow? When is sentience sufficient to require rights?
This seems a rubbery question and I am not sure it reduces to any solid argument. No-one can really know what cows or mice think and how they feel about the world, so doesn't the case from sentience really just reduce to welfarism again? Why does it have to be more? Yes, I've read a few books about this but mostly it just comes down to someone's feeling that sentience demands a rights based recognition. Is there any empirical basis to this claim that doesn't simply reduce to welfarism?