If that were all there were to it, I would consider it almost identical to the death penalty. Someone who was alive, now is not alive.
I would oppose it, even if its effects were limited to that person and had no “leakage” to other people and actions. The guy, in his life, might have done some good. Maybe he had a poem published in an anthology somewhere. I don’t think it’s right to annihilate his entire life history.
Now, the OP also specified that the victim of the crime was not killed. The murderer, by dint of never having existed, never killed.
To me, that’s the big potato in the saucepan. I can bring the victim back to life? I can reduce the overall level of human suffering and misery in this world?
Again, if this were the whole of the deal, then, yes! Fuck yes! The killer never existed, and the victim never died. That’s a great big positive-sum outcome!
Then the question arose of leakage, and how the machine’s effects altered everyone’s life history and experiences, and…that’s when the issue became too muddy to decide easily. With that complication, I’m against it. Bringing one person back to life, at the cost of eliminating everything that’s happened in the last 25 years – all our accomplishments, all our discoveries – is just too great a price to pay.
Yes, sure, many of those accomplishments would be re-accomplished. But not all of them. The little chancy things would very likely come out differently. The outcome of the Super Bowl could very easily be altered. And as for sperm meeting eggs – not one single child born in the subsequent 25 years is the same child! In an obscure sense, you’re saving one murder victim – and murdering some half a billion other children!