Yes and that holds true for all actions—we can never know how our behavior will "sum out" in the future, especially the far far future.

We still make moral decisions based on the imperfect information we have. In fact we have to, because merely existing in the status quo is a moral decision. Even choosing to remove ourselves from existence is a moral decision. On a long enough horizon we can't tell how anything will play out.

So while can't know what any of our decisions or lack of decisions will amount to in the future, we still try, and update our assumptions as time goes on.

But there's no point in arguing whether reducing suffering is moral or not if you're not even going to grant that attempting to reduce suffering is a worthy goal.