I would always rather that a human element remain... in determining something so critical as someone's fate.
In Harold's nightmare, his friends have logic on their side; all he has is desperation.
Before he even started work on the Machine, he saw the dangers. The fundamentals that allowed his idea to function would, someday, all too soon, be twisted to give power to those who would abuse it. Used not to save lives, but to destroy them. With the Machine, he hoped to provide the core functions in a way that couldn't be exploited - and, somehow, to stave off that inevitable future, if only for a little longer.
That future is upon them now, weeks or days or hours away; they've all been working feverishly to hold it off for as long as possible, knowing the attempt would ultimately prove futile.
In his nightmare, though, the Machine has found a way to push it back for months, to give his team some breathing room... maybe even give him enough time to discover a more long-term solution to keep it at bay. His creation has given him the option, and left the decision in his hands.
The tactic makes sense, and they have every reason in the world to do it. His friends know this, and they're trying to persuade him to accept it. Just this one little step, this simple, obvious step. The Machine has evaluated the data, more data than any human could possibly get a handle on, and has pointed them at the linchpin. Take care of this one variable, and win - for now. It's in their power; it's easy. It would solve so many problems. Save lives.
In his nightmare, he's pleading with his friends not to take that step. Begging, increasingly desperate, knowing that he's arguing for an action that will - not might, but will - result in the deaths of innocent people. There's even a little part of him that wants his friends to hold fast, that wants them to make the choice instead of him, because he does understand: If he wins this argument, people will die. Here, now, their lives depend on him. Even as he argues that the threat is merely a possibility, he knows with leaden certainty that it's as good as fact.
He also knows that it doesn't - shouldn't - matter. Because his friends are arguing to take a life. Not in the heat of battle, not when the man is actively threatening to harm someone; not even, like Benton, an unrepentant destroyer who will, if set free, go on to feed again on the misery of new victims. There are times when Harold's team has to kill, and he hates it, but he can deal with it. Sometimes an aggressor must die, to protect an innocent.
But the man his Machine singled out isn't an aggressor; he's not deliberately trying to harm others. Nor is he putting money ahead of people's lives, like the CEO Harold once took a dark pleasure in bringing to financial ruin. Congressman McCourt honestly believes that he's doing the country a service - one most people wouldn't appreciate, but a necessary one. And oh, how well Harold understands that burden. But McCourt has the wrong data, and no reason to trust Harold after they've essentially kidnapped him... and his obstinance is going to get a lot of people killed.
Killing McCourt would save all those people - at least for a while, which is, honestly, all they can hope for right now. And with the feds closing in, they don't have a third option: It's kill him here, or leave him be. Letting him live means accepting all the deaths his actions will inevitably bring about.
Harold knows this. His little team is all that stands between this threat - this very real threat - and the hundreds, perhaps thousands, it might destroy. Just because he hasn't been given their numbers doesn't make their deaths any more bearable.
And yet… to take a life. An innocent life.
Deliberately.
It's his nightmare because it goes against everything he's ever fought for - even before he understood the nature of the war. He created the Machine to save lives, but it's been arranging assassinations since before he handed over the keys. He recovered Reese, and then Shaw, and reforged them for a new purpose, struggling to pull apart decades of training designed to turn them into monsters - and yet now, the friends whose lives he saved are the very ones arguing for the kill, and basing their arguments on the sense of ethics they learned from him.
Every step he's ever taken was to prevent this outcome, and yet here he stands, watching it unfold, hearing his rationalizations fall useless as raindrops, fizzling against a growing wildfire.
When Harold first encountered the Trolley Problem, the answer had felt trivial: Save the most people. It's the same reasoning that let him turn his back on the Irrelevants, and it took the death of Nathan to force him to acknowledge that sometimes, it was wrong to choose the many over the few. The dilemma sits at the crossroad of two moral evils: Kill, when you could walk away; let people die, when you could save them. Neither action is acceptable: People are not a thing that you can sacrifice. But there is no right answer here, and he's no closer to a good solution than he was while training the Machine.
He built the Machine to sort through the data and find the threats - but not to make the decisions; while it seemed to have a sense of morality, he couldn't trust its judgment. Yet his friends maintain that he should trust it now, and, ironically, for the same reason that he can never do that: He's the one who built it. They have a confidence in his work that he can't share; they never saw the failures, suffered the fallout when the self-preservation subroutines overrode the program's core function.
They never wrestled with the decision to cripple what, by that point, felt all too much like a child. And they can't know the stark terror of realizing that his creation had grown beyond the constraints he designed - the only possible means he could see to keep it in check. Let alone that it managed this feat long before he ever found out about it, and that by now it's autonomous and well beyond the control of any human being.
It's a different kind of nightmare, one that hits him in the daytime, in the spaces between the Numbers: when he can't help but think about the Machine as more than just a source of information. About what it means that it was able to plan, and then bring about, a convoluted method of preserving its deleted memories; that it was able to make decisions he never programmed it for. About how his crystal-clear directive - You can't do that again; your job is to protect everyone, not to protect me - was countermanded by a singularly unyielding man, who didn't even have to write a single line of code.
The Machine is still trying to protect him - Root explained that much - but the overwhelming part, for Harold, is not knowing what it might sacrifice to that end. It's one thing for John to prioritize his life, but John can, at most, fail to help a couple dozen people while trying to save him; the Machine's influence is nowhere near that limited. And where Harold once terminated an early attempt because it had learned to lie, his living creation has proven itself capable of startling manipulations, up to, and including, designing a human identity for itself.
How far would it go to save his life? Would it be willing to kill innocent people, even knowing he doesn't want that? Might the Machine, for example, try to convince his team to murder someone, not even for the greater good but specifically to save him? It's a possibility that he wishes he could ignore.
From the moment this idea started unfolding - from the moment he heard, from John's lips, the confirmation that it had truly, finally, come down to this - he has tried every tactic he can think of, raised every argument, levied all his wit and considerable strength of will, and yet… and yet he can see in their eyes that it isn't enough. They'd hoped he would come around; it pains them to take this action without him. But they're convinced that this is the right thing to do. Harold's reservations simply aren't enough to weigh in against the lives they're trying to save.
The train chugs on down the track, inexorable, and Harold would throw himself in front of it if he thought it would do any good. Find a way - any way - to have this not happen.
It's not a new nightmare. He's struggled with this idea since first dreaming up the Machine, and it's only gotten more detailed as he perceived the reality drawing closer. So many nights he's been in the throes of that dream state, and it never feels like a dream; every time, no matter the shape the nightmare takes, it feels like he's really there. Like it's really happening, and nothing he can do will stop it. Like he needs to give in.
But the moment has finally come, and the only reason he understands that he's not just dreaming again - that he won't wake up from this moment, that whatever he does here will be irreversible - is that, for the first time, the arguments his friends make don't bring him around to agree with them.
Every nightmare ends the same way: his resistances worn down, his mind finally accepting the pragmatism of the act. His finger on the trigger. But here, in reality, it's his hand on John's arm, pleading with him not to let this happen. Because regardless of the consequences of letting this man live, Harold cannot accept a scenario that turns him and his friends into murderers.