I watched an online review of The Matrix movie as part of Matrix Month by The Nostalgia Critic. It was an oldie by Internet standards, but it was definitely one of his better reviews, and despite him making clear that he didn't like it, he was as objective as he could be. But if you're a fan of The Nostalgia Critic's work, like I am, you'll notice that what he has in earnestness and film knowledge, he lacks in finer details. And this one in particular, I feel he missed out on.
When asking Agent Schmuck (pfft), a parody representation of both the Matrix's fanboys and the film's own view of itself, why we needed the Matrix, the question is left unanswered because presumably neither the Wachowski's or the fanboys stopped to ponder this. As somebody who studies film signifiers and pop psychology quite obsessively, and as somebody who is neither a Schmuck or a Critic, I believe I can answer this one.
Humans have to be in a Matrix because while they need us unable to resist them physically, they still need us active enough to be able to leech off our energy as optimally as possible.
Everything is energy, and yeah, I get that science likes to categorise types of energy, like kinetic energy, for specific reasons... but energy itself is kinesis. It is CONSTANTLY moving, and the more it moves, the more its output is maximised, especially when we are doing and more importantly thinking, things that make us happy.
Remember Monster's Inc., where it was revealed that laughter generated more energy than fear? That is actually real—what we call "positivity," which is really love, is actually more powerful and generates far more energy than "negativity," fear on a quantum level. The whole point of fear is to protect us, so when we are in fear, the body gathers up as much energy reserves as possible in order to help us flee and fight.
I also read in The Tarot, by Mouni Sadhi, that in the most extreme cases of fear, like a serious illness or sustained trauma, that our energy fields will separate from our bodies, but staying just within "reach," in order to be able to properly heal and protect us, because apparently the body and auric field being too close together when you're sick weakens the auric field, and thus your chances of healing and being protected. Whether or not that's true, the point is, fear drains energy.
Going back to the Matrix, the machines have to prevent extremes. If people were happy all the time, it would only be a matter of time before humans stopped buying it. If we were miserable all the time, it would only be a matter of time before humans decided enough was enough, and as I said before, fear drains energy resources already stockpiled. Complete extremes hitting us immediately, violently wake us up to extremely unpredictable and potentially uncontrollable, effect.
In order for conformity to be necessary, as I said in the Lamb/Wolf Trope essay, equilibrium must be maintained.
The fact that energy moves and it generates the MORE it moves means that some part of human beings MUST be kept active and happy if the Machines are going to siphon off us without us protesting. And the best way to do that is to keep our bodies stationery and our minds busy through distraction, diversion and division (thanks A-Team!).
THAT is why the machines in that movie would need us semi-conscious rather than brain dead. The reason why people keep waking up and the machines seem completely oblivious to the fact that humans are being picked up is because, like all sentient beings that think they are all powerful, the machines stuck to a routine and got complacent.
Also, bear in mind that the Matrix is still being perfected—it is entering into its Seventh reboot when the Matrix trilogy ends, which for me almost mirrors the 7 Ages of an Empire. So of course it's not going to be 100% foolproof. Plus, these things are only just figure out that starting off with abuse never works, because the more violent you are, the quicker people wake up and the more they resist. The Machines hate us but if they want to keep us under control, they have to try as much as possible to CONCEAL that.
The reason why Matrix fanboys or critics haven't thought of this one is because they got caught up and saw the movie as just as a movie. Neo became an Avatar for the Wachowskis and dorks sitting at their screens all day (like me, I admit), and for the critics, it was just a shitty, pretentious movie.
But all media is propaganda speaks Our Master's Voice, especially popular and/or mediocre entertainment, and the more we look at the signifiers, the more the depth of human programming is revealed.
No film critic ever really thinks of this, the Wachowskis didn't think of this, and I doubt even Sophia Stewart, the woman whose work Warner Brothers jacked, thought of this either. But art reveals a lot about subconscious beliefs, subconscious programming, and subconscious knowledge.