Which is exactly why it would be dumb of the writers to do the predictable thing and make him villainous. Much better to have the twist be he's actually heroic in the end.
Not that I'm saying they won't be dumb, but why give the audience exactly what is expected?
Either suggestion sounds predictable and cheesy,
much better IMO to have him simply be mad, or going mad, not villainous, nothing so intentional but reacting to madness, or ptsd, or what have you. A desperate man simply too afraid to go back.