Diamond City appears to have a strong anti-Synth sentiment, to say the least. For instance, shopkeepers will refuse to do business with you if you don’t protest your humanity loudly enough, and then there’s:
The guy who’s about to gun down his brother because he suspects he’s a synth, and then the guards gun him down and loudly declare “this is Diamond City, there are no synths here!” (or something roughly to that effect).
So it seems like a very bad place to be a synth. Yet Nick Valentine is one, runs a prominent business, and seems to be wholly tolerated and non-controversial. That seems out of character for a city that’s already purged a race of nonhumans (ghouls) for…being nonhuman.
Is there any explanation given for the incongruity? I thought that when I got to chat with Valentine I’d get to ask him not just “you’re a synth?” but also “how is it that the people in Diamond City haven’t torn you limb from limb and shoved the pieces in a trash-compactor?”, but that doesn’t eventuate.
Are there any dialog options with other Diamond City NPC’s that shed light on exactly how/why Nick Valentine came to be accepted in a city that seems to be heavily anti-synth (and generally anti-nonhuman)?
If you travel with Nick as a companion, you’ll get dialog sections (just like with any other companion). In one of them he’ll tell you about it:
Nick saved the kidnapped daughter of the mayor, and afterward the mayor sided with him, allowing him to stay in Diamond City even though the population didn’t trust him at first. Eventually, they got used to it.