@maxdancona,
Objective testability is not the measure of relativism.
There is no way to objectively test whether we are in the Matrix. Does that mean that if someone believes he is in the Matrix then it is true for that person that he is in the Matrix? Whether something is objectively testable simply does not determine relativism.
On the belief about perception. I have never tasted feces. Though I believe that I dislike feces, I could discover that feces are actually very delicious to me. Although highly unlikely, and though it may sound very strange, it is conceivable that a person could actually taste something that he perceives as disgusting and yet because of some pathology forms the opinion that he likes it. Perhaps he says, "Oh I love feces!" and actually believes it. But when you give him feces, he spits it out immediately. Silly as it may sound, the distinction is important. Opinion is not the same as perception.
So let's get back to my original point: (1) Each person does not define morality for herself and (2) Each person does not define what belongs to morality for herself.
First, when we talk about Right, we are all talking about the same idea. One person doesn't think - "Oh yes, the Right - Those furry animals!" And another doesn't think - "Oh yes, the Right - You mean those cucumbers?" No, all agree on what the idea of the Right is. Now, it is difficult and perhaps impossible to define. But anyone who thinks the Right is furry animals or cucumbers is simply talking about a different idea than the rest of us.
So (1) Each person does not define morality for herself.
Turning next to (2) Each person does not define what belongs to morality for herself. The definition of the Right, unlike that of Beauty, is not something involving preference or perception. The Right doesn't enter our eyes and bring us pleasure. Some of us dislike the Right. Some of us like the Right. Some gladly admit that they dislike the Right. Some gladly admit that they like the Right. So individual preference is not what defines the Right. This is an entirely different animal than Beauty.
The relativist says - well the right is defined by each person according to their beliefs. So - take the following example:
Franky believes the following:
Hitting a person is wrong.
Joey is a person.
therefore
Hitting Joey is right.
You see that Franky's moral belief system contradicts itself yes? But yet a relativist would say that whatever he defines as Right is Right for him. But what is Right for Franky is contradictory.
Perceptions don't contradict themselves. Opinions and beliefs, conversely, most definitely can contradict themselves.
Additionally, people apply the Right, not only to themselves individually, but also, to everyone else. But this is unlike Beauty. When we're talking about Right and Wrong, we're talking about something that we apply to everyone, not just ourselves individually. So then, Franky might say, "It's wrong for Suzie to hit Joey". But then Harold might say, "It's not wrong for Suzie to hit Joey." This is a contradiction. You can't say that well it's right for Franky and wrong for Harold.
Consider if Franky and Harold applied Beauty to others. Franky says, "Suzie finds the Mona Lisa beautiful." Harold says, "Suzie does not find the Mona Lisa beautiful." This would be a contradiction. This reveals the true nature of relativism. In actuality Beauty is objective. It's not a matter of opinion whether Suzie finds the Mona Lisa beautiful. If it were a matter of opinion, then there would be a contradiction. Harold and Franky cannot both be right.
Therefore (2) Each person does not define what belongs to Morality for herself. This would lead to contradiction.