Smilansky concludes, not that hard determinism is an inaccurate description of the world, but that it is impossible to live justly within a hard deterministic world. Which is the same kind of "null hypothesis" on human welfare as that of antinatalism.
Saul Smilansky, in his paper "Hard Determinism and Punishment: A Practical Reductio," argues that hard determinism fails as a practical moral philosophy, in that it is inherently self-defeating. His core example is the punishment of criminals. Since the hard determinist rejects the notion of morally relevant free will, he rejects the notion that a person can deserve to suffer for his actions (which he could not, in terms of physics, control). While incarceration may be necessary for the purpose of incapacitation (that is, keeping criminals away from the rest of society where they will do harm), it is not justified on grounds of retribution - because, in a hard deterministic world, no one freely chooses anything, so prisoners do not deserve their suffering.
Smilansky proposes that a hard determinist is committed to what he calls "funishment" - resort hotel prisons that accomplish the dual purpose of incapacitating criminals (protecting society) and keeping them entertained (compensating criminals for the injustice necessarily imposed upon them by society, for society's benefit).
The problem with funishment is that it's fun. It ceases to have any effect by way of deterrence. (Here we see three theories of criminal justice interacting in a fascinating way.) Lots of people would want to go to the resort hotel funishment prisons ("fun-zone," Smilansky calls them) and may even commit crimes to get there - removing most of the negative incentive for committing crimes, and in fact creating a positive incentive. The end result of the funishment program is, says Smilansky, "Many people who would otherwise not have become involved in crime, nor even suffer detention, would be caught up in that very life. In the meantime, the rest of us would be living in the worst possible world: suffering unprecedented crime waves while paying unimaginable sums for the upkeep of offenders in opulent institutions of funishment."
Smilansky gives this argument as a reductio of hard determinism as a practical moral philosophy. I think the context of antinatalism makes this an overstatement on Smilansky's part. The upshot of Smilansky's argument is not that hard determinism is not true in the metaphysical sense, but that committing ourselves to its reality ends in moral horror, the "worst possible world." My view is that Smilansky's argument is not a reductio of hard determinism, but of the idea that there could ever be a decently just human society. There is, in essence, a right of each person to be free from unjust suffering - but in fact, unjust suffering is guaranteed simply by being born. See a problem here?
One who recognizes determinism cannot insist on desert. But could a person who accepts hard determinism morally choose to reproduce? By doing so, he imposes suffering on a person who does not deserve it, and will not deserve any of the suffering he receives. Creating a being that will necessarily suffer unjustly seems to me indistinguishable from making a being suffer unjustly. Isn't it immoral to bring beings into an unjust world?
What of fun and pleasure, then? To what extent do we "deserve" those? Can we morally give benefits to people who do not suffer any deprivation without them when other, suffering people need those benefits?
I think that desert is incoherent (and birth wrong) primarily because the most important thing ever to happen to a person, that which determines that he will suffer gravely, is without question outside his free will: his birth. The undeserved suffering imposed on a person simply by being born is likely to overwhelm any suffering justly imposed on him for his actions, even if we were to buy into a morally relevant free will.
But without free will, of course, desert goes out the window. All suffering, none guilty, as Dostoevsky put it. Hard determinism helps us realize the horror show we are in, so that we may end it. THAT, and only that, is the practical consequence. There is no reductio; there is only support for the null hypothesis.
Most self-described compatibilists that I know ground their beliefs in the experience of choices: we feel ourselves to have free choices, and it seems impossible to live as if we didn't. But even granting this, the suffering of the "guilty" is nowhere near justified. A demon could build a machine that we might find ourselves in that would give us the experience of free choice within a virtual reality world. But our suffering as a result of our fake-but-perceived choices would be justified not at all.