In the video below Peter Singer equates morality/ethics with mathematics, which is a concept that I'd never considered before. Most people probably agree that mathematics is objective. It's true independent of our opinions about it. And I can see how it could be argued that morality is exactly the same. In math the understanding that 1+1=2 doesn't instantaneously lead to an understanding of Pi, because although the latter is equally true, coming to understand that it's true is a complicated process. Perhaps the same is true with morality. As with mathematics, morality may be objectively true, but understanding why it's true may be just as complicated as understanding why Pi is true. You don't instantly go from understanding that math exists, to understanding trigonometry, and you don't instantly go from understanding that morality exists, to understanding that slavery is immoral.
Thus there may be an objective morality, but as with math we're still in the process of understanding it, and the fact that we may disagree about what's moral doesn't by necessity mean that morality is subjective. It just means that we don't have a sufficient understanding of morality so as to understand why things are moral, and so instead, morality without God looks subjective, when it really isn't.
And in my opinion, having some God attempting to dictate to me what is and isn't moral will never be as gratifying as actually understanding why things are immoral without a need for that God.