If everything we do is predetermined from the instant of our conception — actually much further back than that since all events leading up to one's conception were also predetermined — then we are all going to still do what we do, which includes judging others by their actions. If some choose not to apply guilt or blame to others, well, then that was also in the cards.
If there is some variable or factor outside our measurable environment that provides for truly free will, then it does make sense for people to be judged based on their actions and for guilt and blame to be applied in appropriate cases.
Applied more generally, if there is no free will then whether an individual believes there is free will does not matter; the deterministic environment decides that matter. If there is free will, then there is a distinct advantage to understanding and believing that fact. So, assuming there is free will has a neutral and upside state, while buying into determinism has a neutral and downside state. Isn't the rational and safe position to just assume there is free will?