As most people are aware, in the not so distant past there were slave owners everywhere around the world, in fact there are still slave owners in some countries. So what does this mean for the person that believes in objective truths. Well, if we consider the Christian bible, this leads to one of two natural conclusions. Either all supporters of slavery in the past are in hell, or all the people currently alive are going to go to hell. This conclusion is logical as at least one of these groups was not adhering to the objective truth and the Bible is pretty clear what happens to sinners.
But, the objectivity absurdity even goes further when we consider theistic doctrines. Every believer past, present and future could all end up going to hell as they never start adhering to the one objective truth about any random important subject. Or, I could be the only person in heaven as I am the only person that by pure chance is doing all the right things to make a god who determines these objective truths happy.
That's why I cannot believe there are still people who think objective morality is rational.
Lastly, if you are an atheist and believe that objective morality exists then you are faced with the same problems as the theist. Although you clearly have no consequences for your mistaken views on morality. But you also have to accept that you can never know what the ideal objective morality is.