while I am someone who thinks a little uncertainty is good i meant it more in the vein of anticipation of deliverance from injustice. it is human nature to want to minimise the suffering experienced even if we believe it will be eventually redressed.
you may believe in the justice system of your country but still wont want to be robbed and while experiencing robbery or violence would still experience the feelings that come with it.
you’re assuming that emotional responses are entirely logical. while there is an element of rationality to all emotions, things like logical inconsistency and the overall picture are often besides the point to the emotion.
nevertheless the religious belief in eventual justice is often a source of solace and help people come out of that emotional state (which is why often athiests posit this as the motivation for religion)
because mourning is not a reaction driven my rational analysis of loss. animals are known to mourn their dead, and there you dont expect reflections about afterlife to play a part in the mourning.
nevertheless there too religion does play a role in helping people reconcile with the tragedy (which is why this is also posited as a reason for the universality of religion).