By value system I mean: postive and negative positions on a spectrum of things that have constant values. The imapct of a behavior can be said to have a negative value, when the one acting on the behavior thinks it is a postive one. An example would be genocide. I'm sure Hitler thought he was doing a great service to humanity, but it doesn't change the fact that his behavior created an immediate and gratuitous suffering among other humans. No one can say with intellectual integrity that his actions were good, or even neutral for that matter. If you do, then your condition is just as real and broken as his.By value system do you mean a rational framework to chose what is appropriate ad what is not? I agree that there is not always a rational framework. We can see this when asked why X is wrong and people say "It just is" or "If you don't see this is wrong there is something wrong with you" or "If you don't understand then I am sure I can't explain it to you."
Inconsistencies in behavior do not make morality subjective, no more than inconsistencies in what makes a person happy determines its subjectivity.