Synths like Nick were people. They know they're a Synth, and they're not trying to replace anyone, really. They take values from whoever was downloaded into their brain, but they still try to be who they want to be, like Nick more or less saying "It's my life now" after you finish his quest.

The ones that just completely replace people and don't know they're robots aren't people. They're just a clone, if anything, and they're more like 'tools' because they don't have their own values. They're just trying to replace someone because they were told to.

That's how I see it and how I judged Synths when playing that game. (>' ')>