Suppose Xander and Willow are each working on the same math problem. They are not cooperating, but they're both working on the same problem. Each of them relies upon their knowledge of mathematics and their ability to perform arithmetic. They differ from one another in terms of both knowledge and ability. Willow is very good at math, but Xander is not, and they come up with different answers.
Suppose now that it wasn't a math problem. Instead, it was a moral question. Once again, they are not cooperating, but they are both working on the same problem. Each of them relies upon their values and their judgment. They differ from one another in terms of both values and judgment, and they come up with different answers.
In both cases, we're talking about a subjective process. Each of them is trapped in their subjectivity, as are we all. Xander can't use Willow's judgment any more than he can use her ability at arithmetic. He's stuck in his own head, with his own judgment. But does that mean the question itself is subjective? Does that mean that there is really no right or wrong answer, and that it is just a matter of opinion?
In the first case, no. There is a right answer, and at least one of them (probably Xander) has gotten it wrong. But in the second case, lots of people want to say that there is no right answer. I think that's wrong. I think morality is every bit as objective as mathematics, but that's argument is beyond the scope of this post. For now, I'm just trying to dispel one particularly bad argument against the idea of objective morality.
I see atheists making this mistake all the time, and it drives me nuts. The argument is that since morality depends on values and values are subjective, morality therefore must be subjective. Morality is based on values, but in the same way that mathematics is based on arithmetic. Values are the process we use to evaluate moral questions, just as arithmetic is a process we use to solve math problems. Different people have different aptitudes for arithmetic, and this explains why different people will come up with different answers to math problems, but that doesn't make math subjective. Similarly, because values are subjective, different individuals will reach different answers to moral questions, but that alone doesn't make morality subjective.