Animals have no rights, and their suffering is morally irrelevant.

[Heffalump]

Of course, anyone can just up and decide on a set of moral axioms for no logical reason at all, and people do it all the time. I even admit that most people do it because "it's how I was raised." But the only way we can decide on axioms that aren't totally subjective is to use reason.

But that's the point. You can't. How could there be an objective starting point? All reason can do is come up with conclusions from whatever premises you assume.

Here's more words regarding that on Moral Relativism:

Metaethical relativists generally suppose that many fundamental moral disagreements cannot be rationally resolved, and on this basis they argue that moral judgments lack the moral authority or normative force that moral objectivists usually contend these judgments may have. Hence, metaethical relativism is in part a negative thesis that challenges the claims of moral objectivists. However, it often involves a positive thesis as well, namely that moral judgments nonetheless have moral authority or normative force, not absolutely or universally (as objectivists contend), but relative to some group of persons such as a society or culture.

Moral objectivists claim that there's a fixed starting point, such as God's law or something external to culture. If one doesn't believe in God's law, one needs another external starting point.
If no such external starting point exists, then you're left with moral relativism which is relative to a group of people in time and place.

[ivan astikov]

There is a fixed starting point for moral objectivists - the point they came up with the concept of moral objectivism.

From my understanding, homo sapiens has been around for about 50-200 thousand years , but as of 3,000 years ago, we were still recording our ideas using crude images on pieces of stone, and the few people smart enough to do this had probably never even considered whether animals should have 'rights', or not.

As mentioned already, until relatively recently, supposedly intelligent men such as Descartes, believed that dogs were akin to machines and could not feel pain.(Although he was more likely a man in denial, trying to alleviate his nightmares. At least, I hope he had nightmares.)

So Vox, maybe you can tell us where moral relativism was hiding for the vast duration of our existence on this planet?

[WhyNot]

Can you at least agree that wanton cruelty to animals is as wrong as talking in the theater? Or are all values of right or wrong determined solely by "rights"?

Yes, all moral wrong is determined by rights. Being annoying in the movie theater is disagreeable, and it will likely cause you social disadvantages, but it is not evil. It's similar for animal cruelty.

Do you think being rude in the movie theater is evil? I think it is merely inadvisable.

I don't often use the word evil seriously. I don't believe I've used it in this thread. Please don't put words into my mouth.

[Exy]

Talking in a movie theater is manifestly evil. It violates the rights of the other patrons -- human beings, Homo agens -- to enjoy a service that they paid for. What could be an act of more acute evil than deliberately confiscating people's property in such a way?

hee hee