There is an approach to all modal logics that says all modal statements are all true and meaningless without appropriate context. If I say X might happen, I need to additionally qualify 'might': What range of possibilities am I talking about? The range in which the Big Bang is possible? Or the range in which black pegasus centaurs rule the world?
In that sense, all moral statements are always both true and meaningless. There is likely to be someone for whom reckless murder is morally obligatory in the presence of blue curtains. If there isn't, we can easily imagine him. He is a fun guy -- if you avoid blue curtains. As a person with maroon curtains, who am I to argue with him? I will just avoid being around both him and blue curtains until the men in white suits take care of him for me.
Your deduction contains a layering of two modalities: necessity and obligation. To be saying anything, you have to inject a context that links the two. Until you say why you think likelihood and morality are linked in this way, your statement is equally true, but meaningless.
Most people do not think the different modalities are very linked at all. In conventional morality there are many things that I should do but won't. And there are even things I should do but can't. If we have agreed that money matters, then when I owe you money, I should pay you. If I can't, that is forgivable but still a minor-league failing to meet an obligation. It has nothing to do with whether or not I ever actually pay you, it has to do with whether we agree on the rules of money.
At the same time, if you consider all statements meaningless that are not descriptions of the past or predictions of the future, that is merely physicalism as a moral position. If you take it seriously, given that most places have a legal system, and consequently nothing motivates you to act on certain modal statements, however meaningless they might be in absolute terms, you will probably eventually end up confined.