For example, think of whatever system of morals (even if purely your own) that you happen to live by. What 'empirical evidence' is there that that code is 'right', or indeed anything other than plain 'wrong'? Surely you wouldn't claim you are a 'moral' person simply on the grounds that as you have managed to stay out of jail (assuming you have) you must be?
Morality does not 'exist' as objects do. Morality is the search for what is right and what is wrong. There is conflict over what is right and what is wrong. Everyone will base their morals on reasoning.
(i.e: I believe it is wrong to murder because it is an infliction on another autonomous human's right to exist willingly.)
The only assumption made here is the assumption that morality is important, but that doesn't require evidence in the way that the assumption that something exists does. Morality requires evidence showing that is is reasonable to apply it (in whichever form) and human history has shown that morality is needed to create a stable human society.
My own moral ideology come from the reasoning that Libertarianism uses, which is 'you have the right to do as you will, providing that does not inflict upon others'. I base it as this:
The Line of Evil
This is the purpose for the application of morality in my view, and why it is necessary.
1. An Individual inflicts upon someone elses right with no justification, or little basis for justification. This is the action.
2. The result of the Infliction of an individual's rights is one which can cause suffering, whether physical or emotional. This is the personal result.
3. The result of suffering is the result of a negative within the society. This is the collective result.
4. This result of the infliction causes suffering. This is Evil.
If 1 does not cause either 2, or 3 it is still an evil. If 2 or 3 is caused from other means, then it is a mistake (therefore morally neutral in purpose) or it is an unhuman in purpose (nature, or if you profess the believe - supernatural)