ok, just looking over the last few posts.
You can believe that there is an objective basis for your position but that it has a high sample variance, large error rate, hard to account for confounding variables, what you are talking about is more qualitative than quantitative, or that there was a misreading when you took your measurements, so believing you are objectively right does not mean you are stuck and cannot have your position changed, and it doesn't mean that you can't be convinced out of the belief that you are objectively correct.
Personal and societal morals can change over time while there is still an objective base to it by there being low level objective morals informed by beliefs or perspective. Think of it like a sense of fairness, which are informed by the individual's model of reality. If you feed into an innate morality your belief that there is an immortal soul that will exist forever and judged by loyalty to a ruler in life, that innate morality might produce a different response than if you feed in a belief that everyone only has one very short life. People objectively have legs (even if you can find a few counter examples) but they can be used to walk, crawl, or run depending on how you use them. From this perspective you can assume everyone's morality is basically the same but that the major differences lay in the models of reality that they are feeding into it, and THAT is where the true differences exist. In the case of abortion it's not that pro-life people believe it's OK to kill babies, that that they don't think that pea sized lumps of undifferentiated cells are babies. I suppose this comes down to an argument of semantics of what is meant by objective vs subjective morality.
objective morality is something completely different than absolute morality, I'm going to assume this has been tackled already.