I am wondering if there is any way to decide wether a decision is moral or not when we can't know the consequences of that decision. In your exemple, as there is no record in humankind history of a world teeming with organized societes controlled by state power in which borders are non-existant, nobody knows for sure what could happen and if this would lead to a better situation or not. Then we might think that it is moral if the intentions are good, if the decision was taken by people after a very long debate and that they judged that it was more likely that unlikely it would be beneficial. But then this reasoning could justify even the worst atrocities , couldn't Hitler actions seen as moral then as he was convinced he was acting for the wealth of German people for exemple. Sure he deliberately intended to kill people and that seems immoral, but what about Churchill's sacrifice of the highlands division because he rightly thought this moved had a positive expected value in terms of casualties in the long run or any of those decisions that you can find in history books. Would we considered those decisions immorals if they had turned in a bad way ? If we open borders do we have to wait 20 years to know if that was moral or no ? That sounds like an impossibility because we need to take the decision in the present . Some would say the moral action is to not act if you are not 100 sure of the outcome but on real life there never is such a situation that you can be that confident with. So I am afraid I have no answer but only more questions ...

The question should be " does moral even exist ".

People tend to take this for granted , but it's a very debatable question. Kant was one of the most ferocious partisan of this theory ( as it is one ), and you could expect some great arguments coming from this brillant mind but in reality they were scarcely convincing. He gave the exemple of having one of your friends knocking at your door and begging you to hide him in your house as for some you unknown reasons he was chased by the police ( you can replace him with jewwish boy and the police with the Nazis to make it more spicy). Then to the question should you lie to the police or no he answers a proud NO, one should never lie, and therefore argues that you should turn your friend down ( or the boy) as this is the moral thing to do and that one should always seek to act in a moral way. This famous episode was to me the evidence that there can't be such thing as moral as it's very easy to come up with those kind of situations that you can't resolve if you believe in moral .