I like Valentine, but he doesn't remember being an institute synth. In fact, every single institute synth has attempted to murder the crap out of me on sight.
So I'm having trouble feeling bad for synths, because I've had no good experiences with them... so why did you join the railroad? Did you meet a synth who needed help somewhere in the game and convince you they could be good people, is there a character who made you want to help them escape?
Maybe we'll get some dlc about synths being on the run, some kind of story to help us see things from their perspective, but for now, what made you decide to help the railroad?