#i gotta say it was the institute – @simplegenius042 on Tumblr

Argument for Railroad:

I don’t think there are any other references to the Institute giving synths fake memories.
There’s no discernible motive for letting loose a synth who doesn’t know he’s a synth in the Capital Wasteland.
The Railroad is operating in the Capital by 2277.
‘Danse’ - brought to you by the people who came up with ‘Harkness’ and ‘Agamemnon?’

Argument for Institute:

The Institute has never had a discernible motive for anything, ever
Danse says his memories came from the Institute.
The Railroad seems to prefer “fun fake memories” to boring, lonely, homeless childhoods.
It’s sad and messed up that Danse still supports killing the Railroad if they saved him. This isn’t really evidence, but it’s true.
’Danse’ - brought to you by the people who came up with ‘Armitage’ and ‘Quentin?’