You’re either being deliberately obtuse or simply don’t understand how species are defined. If you have twins and one is fertile and the other isn't, does that make your wife a monkey? No it means your kid has fertility issues.
Yeah pretty much this. People conflating being a person and experiencing emotion and consciousness on a near human (this can either be a positive or negative) level is beyond irritating. For example, if a dog was suddenly able to communicate about itself and its thoughts in fluent English, its understanding and grasp of various things would be fundamentally different than people as its brain is quite obviously different than a persons and therefore processes information differently than a person. It still feels pain and has an emotional range just like all animals, but its perception of reality is fundamentally different to people due to this. Does this mean they are not deserving of life or possess free will or agency? No it doesn't, but simply saying that anything that possess conscious thought and basic sentience is a person is reductive and ignores fundamental biological differences between sentient species.
The problem with the "lore" Dip Shit Emil (henceforth DSE) is physically impossible. You cannot make something that is indistinguishable from humans in terms of flesh and blood and it not run on food. Biology requires metabolism and metabolism requires FOOD. Also IF this were the case Danse would be shitting a LOT more than his fellows in the BOS and they would put him under intense medical observation.
And then we get to the other impossibility: you cannot make the Synths (capital S means gen 3) indistinguishable without being the same. One, the human body is small to hide the synth component from medical testing, X-rays, cat scans, PET, they have virtual reality teaching machines and memory extracting devices (in the slum part of Boston no less!) they could find a brain implant.
The other more critical thing is that human bodies are not shells, they are ECOSYSTEMS. You have at least 10X the gut bacteria in you by number than cells that are strictly you. If Synths are not biologically human, any rudimentary testing of their stool is gonna show that REAL goddamn quick.
ERGO, Synths are biologically human. It's required secondary powers for their infiltration functions.
So then we get to the reprogramming. Again, the Synth component is the key, it's their non-organic control chip, and probably the thing that implants rudimentary knowledge like how to walk, English language, how to use basic tools, all the things humans have to be socialized into either do at all or do in a way acceptable in a particular culture so you don't end up with adult Romanian Orphan Children.
The synth component is what allows them to be "shut down" and to a degree be reprogrammed as most of identity is memory cores and skillsets, both of which the Institute needs to be able to instantly download into the Synths brain to make them viable workers.
They are sterile because they are sterilized in the birthing matrix, not because they are inhuman or their DNA is incapable. In fact, if lore is logically based on Vault City they should be able to go to any still functional Vault but especially Vault 81, and get lab-grown replacements for their faulty reproductive organs. Dollars to doughnuts the Institute has only screwed with the testes and ovaries because junking the whole reproductive system would be overkill in their minds.