If he's trying to mimic the flavor of Prometheans, then the social penalty is there for a reason... and are almost perfectly appropriate- they'd be able to interact effectively in the short term, but something about prometheans always... just plain disturbed people. If they worked hard at keeping isolated, avoiding social interaction, they could buy time... but one way or another, it always ends in torches and pitchforks. (one variety in particular craved social interaction, and were pretty decent at it, but still came off as 'broken goods' in a big way, and could never actually form non-abusive relationships)
This could arguably just be the effect of an appropriate high-concept... but it needs more, if that's where he wants to go with it.
A flat penalty to all social effects, say, -1 works well IMO... -2 might be a bit heavy, but /shrug.
The only other thing I could think of is some sort of penalty to social consequences (recovering 1 step more slowly, and always being flavored by the 'torches and pitchforks' disquiet caused by not being quite... right, somehow). How does that sound?