system
Given the following post, respond as if you're commenting on Reddit:
human
[The Matrix] Why didn't they just killed people once they got unplugged?

I know that in order for humanity to accept The Matrix they must be offered an "out" at least on a subconscious level. But why don't the Machine just kill every person who decides to get unplugged right then in the pod? 

That they allow them to choose to get out of the Matrix doesn't mean that they have to allow them to run around and fight the Machines?

It looks as if the Machines care more about being "fair" and upholding there end of the deal then being pragmatic because in the end it's the Machine that hold all the power.

EDIT:
To everyone saying they where killing them by flushing them down in to the severs, that's my whole point. If you know that you have to let people leave the Matrix if they want to why use that unsure method of execution via drowning, just run a spike through there skulls while you unplug them and be done with it. Draining them down in to the sewers unharmed is what allows the resistance to pick them up alive and get new soldiers, you can hardly say that one extra action isn't worth crippling the growth of the resistance.
gpt
Basically it's all a matter of ensuring The One returns to the Architect. It's revealed in the Matrix Reloaded that The One is crucial for the survival of The Matrix, that he contains a piece of special code. 

Now the Machines almost certainly know who the One is well in advance and can to a certain extent control his actions. However they cannot create people like Morpheus, humans who are crucial for the growth of The One, training him, educating him and inspiring him so that he can finally reunite with the Architect. 

Now it's conceivable that the native inhabitants of Zion could do the above actions, but at a much greater difficulty and with much greater risk (they don't have the practical experience a Matrix escapee would have). 

In summery people aren't killed when they are unplugged so the support network The One needs to become The One can be created.