Why were living humans used by the Collectors?

Question

In Mass Effect 2 you learn that the reason the Collectors were abducting humans was to turn them into a paste in order to create a Human Reaper.

Considering the Composition of the human body and how the Reapers were beginning to fear Shepard for defeating Sovereign and also the Reapers seemed to operate in the shadows before their invasion, Harbinger abducted living humans rather than just gather the materials from other worlds or even have the Collectors trade for these materials juts like they have done in the past for specimens (did consider the Dragon's Teeth used to create Husks however either a massive war would be needed to get enough bodies or it would just equate to Collectors abductions).

I am wondering, was there something only found inside living humans that was needed for the Human Reaper or was there another reason Harbinger would be needing a sizable and noticeable chunk of the human population (according to EDI's estimates) to create the Human Reaper.

Answer 1

I can only assume its for the same reason that if you put all the chemicals that form a human in a pile it is still not a human. Maybe it needs their souls or electric pulses or DNA. Legion describes them as "billions of organic minds conjoined and uploaded within immortal machine bodies."

A Reaper is not a single entity but rather the collective consciousness of the species used to create it. Individuality is sacrificed so that a species "transcends" to what the Reapers consider a higher form. They must harvest subjects of that species in order to create a Reaper representative of them.

The AI that the Leviathans created was mandated to preserve life. This is how it perceives itself as fulfilling its role. By converting them in to Reapers. Its goal is not to manufacture giant robots.