If morality is universal then why is it that so many Christians disagree on what is/not moral?

Your initial premise must be false.

I'll even take it a step further -- they claim that everything God does is good, because he's God; yet they continually throw away everything we've learned regarding morality and ethics over the last 2000 years in an attempt to square the circle and explain how all the evil things God does in the Bible (e.g.; slavery, genocide, infanticide, punishing children for the sins of their parents) is actually good. That's the absolute height of subjectivity in morality...

Morality is NOT universal. SOME aspects of morality are universal. I'm sure that we'd all agree that killing a young child to harvest its organs would be wrong. But much of what we consider 'morality; is in fact nothing more than cultural traditions. How we arrange our lives though marriage or relationships, for example, is not a moral issue (or should not be). But different cultures have different rules on the subject.

If morality differs at all between cultures geographically or historically, morality is not universal.

Examples: Child brides, homosexuality, polygamy, cannibalism, slavery.

It really makes you wonder what kind of backwards person could genuinely deny that our sense of what we should and should not do, has varied widely over centuries and nations, even with supposedly the same scripture to guide them.

The answer is, Americans and middle easterners.

if you give that power to a human youre in trouble .. imo the only way it works is if you adopt the greatest commandment which is love your neighbor as yourself .. if you do not, then the rules need to be laid down by your human leaders that limit everyone ..